get_name causes a segfault if used with someting other than FunctionSymbol

[PerformanceCoder]

Hi!

Found a bug (crashes terminal immediately) while working with SymEngine. Steps to reproduce:

1. Create file TestPolygon.jl
2. insert this code in TestPolygon:

using SymEngine

x = symbols("x")
mult = sin(2.0*x)
name = get_name(mult) 
print(name)   

3. Launch using julia TestPolygon.jl

After executing this file I get a segfault with repeation rate about 80% (1 of 5 launches completes without errors).

Log file (windows 10, Julia 1.6.1)

Please submit a bug report with steps to reproduce this fault, and any error messages that follow (in their entirety). Thanks.
Exception: EXCEPTION_ACCESS_VIOLATION at 0x7ffc15bf460a -- memcpy at C:\Windows\System32\msvcrt.dll (unknown line)
in expression starting at C:\testpolygon.jl:9
memcpy at C:\Windows\System32\msvcrt.dll (unknown line)
_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPcEEvT_S7_St20forward_iterator_tag.isra.498 at C:\Users\username\.julia\artifacts\635e58d3b6452a234dbf29dbac9259f2a3f7947e\bin\libsymengine-0.8.dll (unknown line)
function_symbol_get_name at C:\Users\username\.julia\artifacts\635e58d3b6452a234dbf29dbac9259f2a3f7947e\bin\libsymengine-0.8.dll (unknown line)
get_name at C:\Users\username\.julia\packages\SymEngine\OE2Ff\src\types.jl:260
jl_apply at /cygdrive/c/buildbot/worker/package_win64/build/src\julia.h:1703 [inlined]
do_call at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:115
eval_value at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:204
eval_stmt_value at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:155 [inlined]
eval_body at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:576
jl_interpret_toplevel_thunk at /cygdrive/c/buildbot/worker/package_win64/build/src\interpreter.c:670
jl_toplevel_eval_flex at /cygdrive/c/buildbot/worker/package_win64/build/src\toplevel.c:877
jl_toplevel_eval_flex at /cygdrive/c/buildbot/worker/package_win64/build/src\toplevel.c:825
jl_toplevel_eval at /cygdrive/c/buildbot/worker/package_win64/build/src\toplevel.c:886 [inlined]
jl_toplevel_eval_in at /cygdrive/c/buildbot/worker/package_win64/build/src\toplevel.c:929
eval at .\boot.jl:360 [inlined]
include_string at .\loading.jl:1094
_include at .\loading.jl:1148
include at .\Base.jl:386
exec_options at .\client.jl:285
_start at .\client.jl:485
jfptr__start_22922.clone_1 at C:\Users\username\AppData\Local\Programs\Julia-1.6.1\lib\julia\sys.dll (unknown line)
jl_apply at /cygdrive/c/buildbot/worker/package_win64/build/src\julia.h:1703 [inlined]
true_main at /cygdrive/c/buildbot/worker/package_win64/build/src\jlapi.c:560
repl_entrypoint at /cygdrive/c/buildbot/worker/package_win64/build/src\jlapi.c:702
mainCRTStartup at /cygdrive/c/buildbot/worker/package_win64/build/cli\loader_exe.c:51
BaseThreadInitThunk at C:\Windows\System32\KERNEL32.DLL (unknown line)
RtlUserThreadStart at C:\Windows\SYSTEM32\ntdll.dll (unknown line)
Allocations: 2648 (Pool: 2638; Big: 10); GC: 0

The problem reproduces in Linux: log file (Manjaro KDE, Julia 1.7.0). Interestingly, I can reproduce it only after 4-5 launches in terminal.

terminate called after throwing an instance of 'std::bad_alloc'
  what():  std::bad_alloc

signal (6): Аварийный останов
in expression starting at /home/username/TestPolygon.jl:5
gsignal at /usr/bin/../lib/libc.so.6 (unknown line)
abort at /usr/bin/../lib/libc.so.6 (unknown line)
__verbose_terminate_handler at /build/gcc/src/gcc/libstdc++-v3/libsupc++/vterminate.cc:95
__terminate at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:48
terminate at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_terminate.cc:58
__cxa_throw at /build/gcc/src/gcc/libstdc++-v3/libsupc++/eh_throw.cc:95
operator new at /build/gcc/src/gcc/libstdc++-v3/libsupc++/new_op.cc:54
_ZNSt7__cxx1112basic_stringIcSt11char_traitsIcESaIcEE12_M_constructIPcEEvT_S7_St20forward_iterator_tag.isra.365 at /home/username/.julia/artifacts/8192a4fc347dc5d7c32b3acfde7af2074fe436a6/lib/libsymengine.so (unknown line)
function_symbol_get_name at /home/username/.julia/artifacts/8192a4fc347dc5d7c32b3acfde7af2074fe436a6/lib/libsymengine.so (unknown line)
get_name at /home/username/.julia/packages/SymEngine/OE2Ff/src/types.jl:260
unknown function (ip: 0x7f206ef675f5)
unknown function (ip: 0x7f206ef66fd4)
unknown function (ip: 0x7f206ef67cb4)
unknown function (ip: 0x7f206ef689d0)
unknown function (ip: 0x7f206ef85287)
unknown function (ip: 0x7f206ef85ebe)
jl_toplevel_eval_in at /usr/bin/../lib/julia/libjulia-internal.so.1 (unknown line)
unknown function (ip: 0x7f2057e00ac7)
unknown function (ip: 0x7f2057f096e1)
unknown function (ip: 0x7f2057f09182)
unknown function (ip: 0x7f2058086ecc)
unknown function (ip: 0x7f2057ff7022)
unknown function (ip: 0x7f2057ff7178)
unknown function (ip: 0x7f206efabd0e)
jl_repl_entrypoint at /usr/bin/../lib/julia/libjulia-internal.so.1 (unknown line)
main at julia (unknown line)
__libc_start_main at /usr/bin/../lib/libc.so.6 (unknown line)
_start at julia (unknown line)
Allocations: 2720 (Pool: 2709; Big: 11); GC: 0
zsh: abort (core dumped)  julia TestPolygon.jl

I understand that "get_name" should be used only with functions, but maybe this code should raise an exception in case of incorrect input?