Fix Unpack example from quickstart segfaults #1100

[Arenoros]

Found the cause of the segfault.

valgrind output before fix

$ g++ main.cpp -I ../../lib/ -O3 -g
$ valgrind ./a.out
==1775== Memcheck, a memory error detector
==1775== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==1775== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==1775== Command: ./a.out
==1775==
"Log message ... 1"
==1775== Invalid read of size 8
==1775==    at 0x10AAB0: operator() (cpp11_zone.hpp:33)
==1775==    by 0x10AAB0: clear (cpp11_zone.hpp:49)
==1775==    by 0x10AAB0: ~finalizer_array (cpp11_zone.hpp:43)
==1775==    by 0x10AAB0: ~zone (cpp11_zone.hpp:196)
==1775==    by 0x10AAB0: operator() (unique_ptr.h:85)
==1775==    by 0x10AAB0: reset (unique_ptr.h:182)
==1775==    by 0x10AAB0: reset (unique_ptr.h:456)
==1775==    by 0x10AAB0: next (unpack.hpp:96)
==1775==    by 0x10AAB0: next (unpack.hpp:92)
==1775==    by 0x10AAB0: next (unpack.hpp:109)
==1775==    by 0x10AAB0: main (main.cpp:155)
==1775==  Address 0x4dea108 is 8 bytes inside a block of size 24 free'd
==1775==    at 0x484BB6F: operator delete(void*, unsigned long) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==1775==    by 0x10AA5F: clear (cpp11_zone.hpp:52)
==1775==    by 0x10AA5F: ~finalizer_array (cpp11_zone.hpp:43)
==1775==    by 0x10AA5F: ~zone (cpp11_zone.hpp:190)
==1775==    by 0x10AA5F: operator() (unique_ptr.h:85)
==1775==    by 0x10AA5F: reset (unique_ptr.h:182)
==1775==    by 0x10AA5F: reset (unique_ptr.h:456)
==1775==    by 0x10AA5F: next (unpack.hpp:96)
==1775==    by 0x10AA5F: next (unpack.hpp:92)
==1775==    by 0x10AA5F: next (unpack.hpp:109)
==1775==    by 0x10AA5F: main (main.cpp:155)
==1775==  Block was alloc'd at
==1775==    at 0x4849013: operator new(unsigned long) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
==1775==    by 0x10ACA2: push (cpp11_zone.hpp:58)
==1775==    by 0x10ACA2: push_finalizer (cpp11_zone.hpp:270)
==1775==    by 0x10ACA2: flush_zone (unpack.hpp:136)
==1775==    by 0x10ACA2: release_zone (unpack.hpp:114)
==1775==    by 0x10ACA2: next (unpack.hpp:96)
==1775==    by 0x10ACA2: next (unpack.hpp:92)
==1775==    by 0x10ACA2: next (unpack.hpp:109)
==1775==    by 0x10ACA2: main (main.cpp:155)
==1775==
==1775== Invalid read of size 8
==1775==    at 0x10AAB4: operator() (cpp11_zone.hpp:33)
==1775==    by 0x10AAB4: clear (cpp11_zone.hpp:49)
==1775==    by 0x10AAB4: ~finalizer_array (cpp11_zone.hpp:43)
==1775==    by 0x10AAB4: ~zone (cpp11_zone.hpp:196)
==1775==    by 0x10AAB4: operator() (unique_ptr.h:85)
==1775==    by 0x10AAB4: reset (unique_ptr.h:182)
==1775==    by 0x10AAB4: reset (unique_ptr.h:456)
==1775==    by 0x10AAB4: next (unpack.hpp:96)
==1775==    by 0x10AAB4: next (unpack.hpp:92)
==1775==    by 0x10AAB4: next (unpack.hpp:109)
==1775==    by 0x10AAB4: main (main.cpp:155)
==1775==  Address 0x4dea100 is 0 bytes inside a block of size 24 free'd
==1775==    at 0x484BB6F: operator delete(void*, unsigned long) (in /usr/libexec/valgrind/vgpreload_memcheck-amd64-linux.so)
....
==1775==
==1775==
==1775== HEAP SUMMARY:
==1775==     in use at exit: 0 bytes in 0 blocks
==1775==   total heap usage: 16 allocs, 19 frees, 148,190 bytes allocated
==1775==
==1775== All heap blocks were freed -- no leaks are possible
==1775==
==1775== For lists of detected and suppressed errors, rerun with: -s
==1775== ERROR SUMMARY: 38 errors from 12 contexts (suppressed: 0 from 0)

valgrind output after

$ g++ main.cpp -I ../../lib/ -O3 -g
$ valgrind ./a.out
==1797== Memcheck, a memory error detector
==1797== Copyright (C) 2002-2017, and GNU GPL'd, by Julian Seward et al.
==1797== Using Valgrind-3.18.1 and LibVEX; rerun with -h for copyright info
==1797== Command: ./a.out
==1797==
"Log message ... 1"
"Log message ... 2"
"Log message ... 3"
==1797==
==1797== HEAP SUMMARY:
==1797==     in use at exit: 0 bytes in 0 blocks
==1797==   total heap usage: 16 allocs, 16 frees, 148,190 bytes allocated
==1797==
==1797== All heap blocks were freed -- no leaks are possible
==1797==
==1797== For lists of detected and suppressed errors, rerun with: -s
==1797== ERROR SUMMARY: 0 errors from 0 contexts (suppressed: 0 from 0)

Checked with g++ 11.4.0

[redboltz]

It seems that sCI reports errors. Could you fix it?
Maybe zlib version updating required.