Repository: godot
Issue: Godot crashes due to `Animation` is null pointer.
Labels: bug,topic:editor,confirmed,crash,topic:animation

### Godot version

Godot Engine v4.2.dev.custom_build (c5a7462a00a665a72c7c1a746c105e3c1c475c96)

### System information

Arch Linux, AMD ATI Radeon Vega Series / Radeon Vega Mobile Series, CPU: AMD Ryzen 3 3200G (4) @ 3.600GHz

### Issue description

Somehow in `scene/animation/animation_player.cpp:1013`, `cd.from->animation` is a null pointer when there is an `AnimationPlayer` in a child scene like given minimal reproduction project. 

- This only happens in the editor.
- This only happens when the evil scene is the first scene being edited (following the tabs).

```
================================================================
handle_crash: Program crashed with signal 11
Engine version: Godot Engine v4.2.dev.custom_build (c5a7462a00a665a72c7c1a746c105e3c1c475c96)
Dumping the backtrace. Please include this when reporting the bug to the project developer.
[1] /usr/lib/libc.so.6(+0x3e710) [0x7f774ec3e710] (??:0)
[2] Animation::get_length() const (/home/rechie/Documents/cxx_projects/gobread/scene/resources/animation.cpp:3711)
[3] AnimationPlayer::_animation_process_data(AnimationPlayer::PlaybackData&, double, float, bool, bool) (/home/rechie/Documents/cxx_projects/gobread/scene/animation/animation_player.cpp:1013)
[4] AnimationPlayer::_animation_process2(double, bool) (/home/rechie/Documents/cxx_projects/gobread/scene/animation/animation_player.cpp:1110)
[5] AnimationPlayer::_animation_process(double) (/home/rechie/Documents/cxx_projects/gobread/scene/animation/animation_player.cpp:1281)
[6] AnimationPlayer::_notification(int) (/home/rechie/Documents/cxx_projects/gobread/scene/animation/animation_player.cpp:250)
[7] AnimationPlayer::_notificationv(int, bool) (/home/rechie/Documents/cxx_projects/gobread/scene/animation/animation_player.h:66)
[8] Object::notification(int, bool) (/home/rechie/Documents/cxx_projects/gobread/core/object/object.cpp:798)
[9] SceneTree::_process_group(SceneTree::ProcessGroup*, bool) (/home/rechie/Documents/cxx_projects/gobread/scene/main/scene_tree.cpp:947)
[10] SceneTree::_process(bool) (/home/rechie/Documents/cxx_projects/gobread/scene/main/scene_tree.cpp:1027)
[11] SceneTree::process(double) (/home/rechie/Documents/cxx_projects/gobread/scene/main/scene_tree.cpp:508)
[12] Main::iteration() (/home/rechie/Documents/cxx_projects/gobread/main/main.cpp:3467)
[13] OS_LinuxBSD::run() (/home/rechie/Documents/cxx_projects/gobread/platform/linuxbsd/os_linuxbsd.cpp:933)
[14] /home/rechie/Documents/cxx_projects/gobread/bin/godot.linuxbsd.editor.dev.x86_64.llvm(main+0x1d3) [0x564c2b4e9663] (/home/rechie/Documents/cxx_projects/gobread/platform/linuxbsd/godot_linuxbsd.cpp:76)
[15] /usr/lib/libc.so.6(+0x27cd0) [0x7f774ec27cd0] (??:0)
[16] /usr/lib/libc.so.6(__libc_start_main+0x8a) [0x7f774ec27d8a] (??:0)
[17] /home/rechie/Documents/cxx_projects/gobread/bin/godot.linuxbsd.editor.dev.x86_64.llvm(_start+0x25) [0x564c2b4e93b5] (??:?)
-- END OF BACKTRACE --
================================================================
```

I have tried adding
```
ERR_FAIL_COND(cd.from->animation == nullptr); // Line 1012
```
And it screams
```
...
ERROR: Condition "cd.from->animation == nullptr" is true.
   at: _animation_process_data (scene/animation/animation_player.cpp:1013)
ERROR: Condition "cd.from->animation == nullptr" is true.
   at: _animation_process_data (scene/animation/animation_player.cpp:1013)
ERROR: Condition "cd.from->animation == nullptr" is true.
   at: _animation_process_data (scene/animation/animation_player.cpp:1013)
ERROR: Condition "cd.from->animation == nullptr" is true.
   at: _animation_process_data (scene/animation/animation_player.cpp:1013)
ERROR: Condition "cd.from->animation == nullptr" is true.
   at: _animation_process_data (scene/animation/animation_player.cpp:1013)
```

### Steps to reproduce

Open minimal reproduction project in Godot editor.

### Minimal reproduction project

[godot_crash.zip](https://github.com/godotengine/godot/files/12369008/godot_crash.zip)