Monospace image font import completely broken in 4.3.dev6

[jummy0]

Tested versions

• Reproducible in 4.3.dev6

System information

Godot v4.3.dev6 - Windows 10.0.19045 - GLES3 (Compatibility) - AMD Radeon R7 M440 (Advanced Micro Devices, Inc.; 27.20.20913.2000) - Intel(R) Core(TM) i7-7500U CPU @ 2.70GHz (4 Threads)

Issue description

Monospace image fonts completely fail to import under v4.3.dev6. All characters are placeholder rectangles. No error in output. Image fonts from a previous version work fine, but break when re-imported in v4.3.dev6.

Steps to reproduce

1. import a monospace image font in v4.3.dev6
2. observe the font failing to appear

Minimal reproduction project (MRP)

monospace-image-font-import-test-for-v4.3.dev6.zip

[bruvzg]

Should be fixed by #90647