Repository: godot
Issue: Crash when unwrapping mesh with blend shapes
Labels: bug,topic:editor,topic:import,crash,topic:3d

### Godot version

3.5.2.stable

### System information

Manjaro Linux amd64

### Issue description

I wanted to quickly test lightmap baking on an older 3D project, so I set "Light Baking" to "Gen Lightmaps" in the import settings for all glTF models, and hit Reimport. The import got to a particular object, and crashed.

If `.import/` is deleted or lost after this change, the editor crashes every time the project is loaded. I have to manually remove `meshes/light_baking=2` from the relevant `**.gltf.import` files.

Seems like the crash might be related to the mesh in question having blend shapes. I reimported a bunch of other meshes, which don't have blend shapes, and they worked fine. Ultimately I'm not sure though.

This is the output from the minimal repro project:
```
Godot Engine v3.5.2.stable.official.170ba337a - https://godotengine.org
OpenGL ES 3.0 Renderer: AMD Radeon RX 5700 XT (navi10, LLVM 15.0.7, DRM 3.52, 6.3.5-2-MANJARO)
Async. shader compilation: OFF
 
WARNING: Octahedral compression cannot be used to compress a zero-length vector, please use normalized normal values or disable octahedral compression
     at: norm_to_oct (servers/visual_server.cpp:346)
ERROR: Can't unwrap mesh with blend shapes.
   at: lightmap_unwrap_cached (scene/resources/mesh.cpp:1065)

================================================================
handle_crash: Program crashed with signal 11
Engine version: Godot Engine v3.5.2.stable.official (170ba337a5d9e4c1e40d63b89dc1ba297b71860b)
Dumping the backtrace. Please include this when reporting the bug to the project developer.
[1] /usr/lib/libc.so.6(+0x39ab0) [0x7f6f34b10ab0] (??:0)
[2] godot3() [0x199a5fb] (??:0)
[3] godot3() [0x1562348] (??:0)
[4] godot3() [0x1565e98] (??:0)
[5] godot3() [0x178a857] (??:0)
[6] godot3() [0x178b630] (??:0)
[7] godot3() [0xab3bf9] (??:0)
[8] godot3() [0x2e7e229] (??:0)
[9] godot3() [0x2e895ea] (??:0)
[10] godot3() [0x200b93a] (??:0)
[11] godot3() [0x200ca03] (??:0)
[12] godot3() [0x200cfbb] (??:0)
[13] godot3() [0x17a16e5] (??:0)
[14] godot3() [0x2e7ddd7] (??:0)
[15] godot3() [0x201fbc1] (??:0)
[16] godot3() [0x2026271] (??:0)
[17] godot3() [0x2028595] (??:0)
[18] godot3() [0x202886b] (??:0)
[19] godot3() [0xd487e5] (??:0)
[20] godot3() [0x2e7e229] (??:0)
[21] godot3() [0x2e7015e] (??:0)
[22] godot3() [0x1fbbcdb] (??:0)
[23] godot3() [0x1fd4d00] (??:0)
[24] godot3() [0xa43305] (??:0)
[25] godot3() [0xa44549] (??:0)
[26] godot3() [0xa49654] (??:0)
[27] godot3() [0xa03f74] (??:0)
[28] /usr/lib/libc.so.6(+0x23850) [0x7f6f34afa850] (??:0)
[29] /usr/lib/libc.so.6(__libc_start_main+0x8a) [0x7f6f34afa90a] (??:0)
[30] godot3() [0xa168ce] (??:0)
-- END OF BACKTRACE --
================================================================
Aborted (core dumped)
```

### Steps to reproduce

1. Create 3D model with blend shapes, export to glTF
2. Import model in Godot
3. In model's import settings, set "Light Baking" to "Gen Lightmaps"
4. Reimport

or

1. Load minimal repro project (it crashes on initial import, since "Gen Lightmaps" is already set)

### Minimal reproduction project

[unwrap-crash-repro.zip](https://github.com/godotengine/godot/files/11924828/unwrap-crash-repro.zip)