Crash when click on an AnimationTree node that contains an invalid node.

[fabriceci]

Godot version

4.0 8b3b274

System information

MacOS 11.4

Issue description

When I click on the tree on the AnimationTree node, the editor crash.

The three contains an invalid node as I see in the console:

ERROR: Condition "!p_node.is_valid()" is true. Returning: 0
   at: _blend_node (scene/animation/animation_tree.cpp:178)

Steps to reproduce

Click on the node.

Minimal reproduction project

I found this by checking this project: https://github.com/TokageItLab/3d-platform-test-for-godot4

Open the project, open the Player scene, click on the AnimationTree node.

[qarmin]

ERROR: Condition "!p_node.is_valid()" is true. Returning: 0
   at: _blend_node (scene/animation/animation_tree.cpp:178)
editor/plugins/animation_blend_tree_editor_plugin.cpp:132:39: runtime error: member access within null pointer of type 'struct AnimationNode'
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] godot4s() [0x21a85e0] (/mnt/Miecz/godot/platform/linuxbsd/crash_handler_linuxbsd.cpp:54)
[2] /lib/x86_64-linux-gnu/libc.so.6(+0x41040) [0x7f99f26cc040] (??:0)
[3] AnimationNodeBlendTreeEditor::_update_graph() (/mnt/Miecz/godot/editor/plugins/animation_blend_tree_editor_plugin.cpp:132 (discriminator 5))
[4] AnimationNodeBlendTreeEditor::edit(Ref<AnimationNode> const&) (/mnt/Miecz/godot/editor/plugins/animation_blend_tree_editor_plugin.cpp:874 (discriminator 6))
[5] AnimationTreeEditor::edit_path(Vector<String> const&) (/mnt/Miecz/godot/editor/plugins/animation_tree_editor_plugin.cpp:121)
[6] AnimationTreeEditor::_notification(int) (/mnt/Miecz/godot/editor/plugins/animation_tree_editor_plugin.cpp:153 (discriminator 3))
[7] AnimationTreeEditor::_notificationv(int, bool) (/mnt/Miecz/godot/editor/plugins/animation_tree_editor_plugin.h:52 (discriminator 14))
[8] Object::notification(int, bool) (/mnt/Miecz/godot/core/object/object.cpp:843)
[9] SceneTree::_notify_group_pause(StringName const&, int) (/mnt/Miecz/godot/scene/main/scene_tree.cpp:851)
[10] SceneTree::process(double) (/mnt/Miecz/godot/scene/main/scene_tree.cpp:453 (discriminator 4))
[11] Main::iteration() (/mnt/Miecz/godot/main/main.cpp:2542)
[12] OS_LinuxBSD::run() (/mnt/Miecz/godot/platform/linuxbsd/os_linuxbsd.cpp:342)
[13] godot4s(main+0x40b) [0x21a60b1] (/mnt/Miecz/godot/platform/linuxbsd/godot_linuxbsd.cpp:60)
[14] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0xd5) [0x7f99f26b3565] (??:0)
[15] godot4s(_start+0x2e) [0x21a5bee] (??:?)
-- END OF BACKTRACE --