### Godot version

Godot Engine v4.0.beta16.official.518b9e580

### System information

Linux, Vulkan, nvidia RTX 2070, Driver 525.60.11

### Issue description

Editor crashes when changing between theme editor and animation editor

Console:
`ERROR: Condition "slot >= slot_max" is true. Returning: nullptr
   at: get_instance (./core/object/object.h:962)
ERROR: Condition "slot >= slot_max" is true. Returning: nullptr
   at: get_instance (./core/object/object.h:962)

================================================================
handle_crash: Program crashed with signal 11
Engine version: Godot Engine v4.0.beta16.official (518b9e5801a19229805fe837d7d0cf92920ad413)
Dumping the backtrace. Please include this when reporting the bug to the project developer.
[1] /lib/x86_64-linux-gnu/libc.so.6(+0x42520) [0x7f908134c520] (??:0)
[2] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x1c6d494] (??:0)
[3] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x1c4eefe] (??:0)
[4] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x44fb21a] (??:0)
[5] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x26faf8b] (??:0)
[6] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x448c994] (??:0)
[7] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2a9eb11] (??:0)
[8] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2a9eb8f] (??:0)
[9] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x1c65ae0] (??:0)
[10] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x42e50c2] (??:0)
[11] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x44fb21a] (??:0)
[12] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2bcf06f] (??:0)
[13] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2bcfa7e] (??:0)
[14] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2b30f15] (??:0)
[15] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2b817d5] (??:0)
[16] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2b85781] (??:0)
[17] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2b85deb] (??:0)
[18] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x2ba1cf5] (??:0)
[19] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0xe69114] (??:0)
[20] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x42d5f34] (??:0)
[21] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0x42d6db5] (??:0)
[22] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0xe6ab2d] (??:0)
[23] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0xddd7c2] (??:0)
[24] /lib/x86_64-linux-gnu/libc.so.6(+0x29d90) [0x7f9081333d90] (??:0)
[25] /lib/x86_64-linux-gnu/libc.so.6(__libc_start_main+0x80) [0x7f9081333e40] (??:0)
[26] /home/solorvox/GameDev/godot-engine/Godot_v4.0-beta16_linux.x86_64() [0xdfd8ee] (??:0)
-- END OF BACKTRACE --
================================================================`


### Steps to reproduce

Open included project
1) Click on AnimationPlayer in scene tree
2) Click on TextureRect in scene tree
4) Click on "Theme" editor at bottom of editor window (theme editor opens)
5) Click on "Animation" editor at bottom (crash)

Notes: The shader source code must be open, and a theme must be open to repeat this crash

### Minimal reproduction project

[animation-crash.zip](https://github.com/godotengine/godot/files/10530646/animation-crash.zip)

Button *get_pause_button() { return pause_button; }
	Button *add_bottom_panel_item(String p_text, Control *p_item);
	void make_bottom_panel_item_visible(Control *p_item);
	void raise_bottom_panel_item(Control *p_item);
	void hide_bottom_panel();
	void remove_bottom_panel_item(Control *p_item);
	Variant drag_resource(const Ref<Resource> &p_res, Control *p_from);
	Variant drag_files_and_dirs(const Vector<String> &p_paths, Control *p_from);
	void add_tool_menu_item(const String &p_name, const Callable &p_callback);
	void add_tool_submenu_item(const String &p_name, PopupMenu *p_submenu);
	void remove_tool_menu_item(const String &p_name);
	PopupMenu *get_export_as_menu();
	void save_all_scenes();
	void save_scene_list(Vector<String> p_scene_filenames);
	void restart_editor();
	void notify_settings_changed();
	void dim_editor(bool p_dimming);
	bool is_editor_dimmed() const;
	void edit_current() { _edit_current(); };