Crash when the skeleton of a Polygon2d was removed

[ghost]

Godot version:
v3.1.dev.calinou.6c569c9

OS/device including version:
Ubuntu 18.04

Issue description:
Godot Engine crashed and close when the skeleton of a Polygon2d was removed,

Steps to reproduce:
Add a Skeleton2d to a Polygon2d, sync bones, then paint vertex and then try to remove the skeleton clicking the "Broom" icon of Polygon2D's Skeleton property in the inspector.

Minimal reproduction project:
polygon2d.zip

[reduz]

I can't reproduce. I added some extra checks but still not sure how this could cause a crash. More information or trying to reproduce the crash with a more recent build would be appreciated.

[ghost]

Well, that's weird. I download the most recent build and the same file above, and make the same things.
When I click the broom icon, the editor closes.

Output:

handle_crash: Program crashed with signal 11
Dumping the backtrace. Please include this when reporting the bug on https://github.com/godotengine/godot/issues
[1] /lib/x86_64-linux-gnu/libc.so.6(+0x3ef20) [0x7f9016d39f20] (??:0)
[2] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x1470ad4] (??:0)
[3] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x1470d59] (??:0)
[4] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x18a13ea] (??:0)
[5] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x18a6647] (??:0)
[6] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x22a0934] (??:0)
[7] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x18154e9] (??:0)
[8] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x489ea5] (??:0)
[9] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x22a56ee] (??:0)
[10] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x226da41] (??:0)
[11] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x226dcdf] (??:0)
[12] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x145b5ec] (??:0)
[13] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x435ebf] (??:0)
[14] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x421841] (??:0)
[15] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x41403f] (??:0)
[16] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xe7) [0x7f9016d1cb97] (??:0)
[17] /tmp/.mount_godot-bN0wfc/usr/bin/godot() [0x4178cf] (??:0)
-- END OF BACKTRACE --

Also happen when I try to do this, from a new project.

[akien-mga]

I can reproduce it with the provided project and the steps to reproduce (click the "Broom" icon of Polygon2D's Skeleton property in the inspector).

Stacktrace:

Thread 1 "godot-git" received signal SIGSEGV, Segmentation fault.
0x000000000277b83b in Node::_get_node (this=0x0, p_path=...) at scene/main/node.cpp:1238
1238            if (!data.inside_tree && p_path.is_absolute()) {
#0  0x000000000277b83b in Node::_get_node (this=0x0, p_path=...) at scene/main/node.cpp:1238
        __FUNCTION__ = "_get_node"
        current = 0x12c7e0e0
        root = 0x12c7e0e0
#1  0x000000000277bee9 in Node::has_node (this=0x0, p_path=...) at scene/main/node.cpp:1311
No locals.
#2  0x0000000002e186e0 in Polygon2D::_notification (this=0x12be2330, p_what=30) at scene/2d/polygon_2d.cpp:215
        bone = 0xf24f70 <_start>
        bone_index = 32767
        r = {<PoolVector<float>::Access> = {_vptr.Access = 0x0, alloc = 0x100000000000000, mem = 0x174aba90}, <No data fields>}
        i = 0
        vc = 8
        bonesw = 0x12c7e050
        weightsw = 0xe083dd0
        bones = {_cowdata = 0x12bbf020, write = {_parent = 0x12bbf020}}
        weights = {_cowdata = 0x12c7e0e0, write = {_parent = 0x12c7e0e0}}
        len = 8
        colors = {_cowdata = 0x7fffffffbf30, write = {_parent = 0x7fffffffbf30}}
        color_len = 235431384
        skeleton_node = 0x0
        points = {_cowdata = 0x12c7e160, write = {_parent = 0x12c7e160}}
        uvs = {_cowdata = 0xe084940, write = {_parent = 0xe084940}}
#3  0x0000000002e20c41 in Polygon2D::_notificationv (this=0x12be2330, p_notification=30, p_reversed=false) at scene/2d/polygon_2d.h:38
No locals.
#4  0x000000000405e1ac in Object::notification (this=0x12be2330, p_notification=30, p_reversed=false) at core/object.cpp:978
No locals.
#5  0x0000000002e47e80 in CanvasItem::_update_callback (this=0x12be2330) at scene/2d/canvas_item.cpp:339
No locals.
#6  0x000000000100037e in MethodBind0::call (this=0x6806790, p_object=0x12be2330, p_args=0x0, p_arg_count=0, r_error=...) at core/method_bind.gen.inc:54
        instance = 0x12be2330
        __FUNCTION__ = "call"
#7  0x000000000405dfe7 in Object::call (this=0x12be2330, p_method=..., p_args=0x0, p_argcount=0, r_error=...) at core/object.cpp:968
        __FUNCTION__ = "call"
        ret = {type = Variant::NIL, _data = {_bool = 32, _int = 93029152, _real = 4.5962508064943493e-316, _transform2d = 0x58b8320 <Memory::mem_usage>, 
            _aabb = 0x58b8320 <Memory::mem_usage>, _basis = 0x58b8320 <Memory::mem_usage>, _transform = 0x58b8320 <Memory::mem_usage>, _ptr = 0x58b8320 <Memory::mem_usage>, 
            _mem = " \203\213\005\000\000\000\000\000\030U\027\020\000\000\001"}}
        _debug_lock = {obj = 0x12be2330}
        method = 0x6806790
#8  0x00000000041027da in MessageQueue::_call_function (this=0x5a0fa60, p_target=0x12be2330, p_func=..., p_args=0x7fffef8e7038, p_argcount=0, p_show_error=false)
    at core/message_queue.cpp:256
        argptrs = 0x0
        ce = {error = Variant::CallError::CALL_OK, argument = 67540140, expected = Variant::NIL}
        __FUNCTION__ = "_call_function"
#9  0x0000000004102a2e in MessageQueue::flush (this=0x5a0fa60) at core/message_queue.cpp:300
#10 0x00000000027e4b7d in SceneTree::iteration (this=0x6e34a50, p_time=0.0166666675) at scene/main/scene_tree.cpp:476
#11 0x0000000000f61f16 in Main::iteration () at main/main.cpp:1773
#12 0x0000000000f33415 in OS_X11::run (this=0x7fffffffd2d0) at platform/x11/os_x11.cpp:2695
#13 0x0000000000f2511b in main (argc=2, argv=0x7fffffffda38) at platform/x11/godot_x11.cpp:55

[ibrahn]

In Polygon2D's draw notification handling:

godot/scene/2d/polygon_2d.cpp

Line 215 in 94403af

if (!skeleton_node->has_node(bone_weights[i].path)) {

Crashes because no skeleton is set.

It's guarded by this:

godot/scene/2d/polygon_2d.cpp

Lines 197 to 198 in 94403af

	if (!invert && bone_weights.size()) {
	//a skeleton is set! fill indices and weights

Is it fine to just check the skeleton node here or should we be clearing the bone weights when the skeleton is unset?