On some hardware/systems, blender may crash when adding, rendering or displaying Grease Pencil objects.
In `/source/blender/draw/engines/gpencil/shaders/gpencil_vert.glsl`, line 35:
```
gpMaterialFlag gp_flag = floatBitsToInt(gp_mat._flag);
```
`gpMaterialFlag` is of type `uint`. This is a mismatched-type assignment that can cause crashes on some hardware/systems with GLSL that do not support implicit type casting.
So use `floatBitsToUint` for type conversion.
Differential Revision: https://developer.blender.org/D15433
93253d5dcc