Editor crash in TileSet::tile_get_shape(int, int)

[qarmin]

Godot version:
3.2.dev.custom_build. 974b07f

OS/device including version:
Ubuntu 19.04

Issue description:

[1] /lib/x86_64-linux-gnu/libc.so.6(+0x43f60) [0x7f5cf4077f60] (??:0)
[2] CowData<TileSet::ShapeData>::get(int) const (/home/rafal/Pulpit/godot/./core/cowdata.h:151 (discriminator 7))
[3] Vector<TileSet::ShapeData>::operator[](int) const (/home/rafal/Pulpit/godot/./core/vector.h:85)
[4] TileSet::tile_get_shape(int, int) const (/home/rafal/Pulpit/godot/scene/resources/tile_set.cpp:732)
[5] MethodBind2RC<Ref<Shape2D>, int, int>::call(Object*, Variant const**, int, Variant::CallError&) (/home/rafal/Pulpit/godot/./core/method_bind.gen.inc:2105 (discriminator 13))
[6] Object::call(StringName const&, Variant const**, int, Variant::CallError&) (/home/rafal/Pulpit/godot/core/object.cpp:940 (discriminator 1))
[7] Variant::call_ptr(StringName const&, Variant const**, int, Variant*, Variant::CallError&) (/home/rafal/Pulpit/godot/core/variant_call.cpp:1073 (discriminator 1))
[8] GDScriptFunction::call(GDScriptInstance*, Variant const**, int, Variant::CallError&, GDScriptFunction::CallState*) (/home/rafal/Pulpit/godot/modules/gdscript/gdscript_function.cpp:1080)
[9] GDScriptInstance::call_multilevel(StringName const&, Variant const**, int) (/home/rafal/Pulpit/godot/modules/gdscript/gdscript.cpp:1192)
[10] Node::_notification(int) (/home/rafal/Pulpit/godot/scene/main/node.cpp:58)
[11] Node::_notificationv(int, bool) (/home/rafal/Pulpit/godot/./scene/main/node.h:46 (discriminator 14))
[12] CanvasItem::_notificationv(int, bool) (/home/rafal/Pulpit/godot/./scene/2d/canvas_item.h:166 (discriminator 3))
[13] Node2D::_notificationv(int, bool) (/home/rafal/Pulpit/godot/./scene/2d/node_2d.h:38 (discriminator 3))
[14] Object::notification(int, bool) (/home/rafal/Pulpit/godot/core/object.cpp:952)
[15] SceneTree::_notify_group_pause(StringName const&, int) (/home/rafal/Pulpit/godot/scene/main/scene_tree.cpp:975)
[16] SceneTree::idle(float) (/home/rafal/Pulpit/godot/scene/main/scene_tree.cpp:522 (discriminator 3))
[17] Main::iteration() (/home/rafal/Pulpit/godot/main/main.cpp:1922)
[18] OS_X11::run() (/home/rafal/Pulpit/godot/platform/x11/os_x11.cpp:3163)
[19] /usr/bin/godot(main+0xdf) [0x138d871] (/home/rafal/Pulpit/godot/platform/x11/godot_x11.cpp:56)
[20] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xeb) [0x7f5cf405ab6b] (??:0)
[21] /usr/bin/godot(_start+0x2a) [0x138d6da] (??:?)

Steps to reproduce:

1. Run minimal project and wait

Minimal reproduction project:
https://github.com/qarmin/The-worst-Godot-test-project/
commit ff73254afc2a04103dfd577961fbf2541e4586aa
ZIP - https://github.com/qarmin/The-worst-Godot-test-project/archive/ff73254afc2a04103dfd577961fbf2541e4586aa.zip

[Zireael07]

@qarmin you're a crash-finding machine xD