Text rendering corrupted - rendering as black rects

[caspark]

Sometimes text rendering breaks in such a way that all text characters are rendered as filled black rects (regardless of color used to draw the text); the black rects approximately match the bounding boxes of the characters.

Some details:

• Happens on both my integrated AMD GPU on Linux and dedicated Nvidia GPU on Windows
• I am just using the default font (and never load another)
• Haven't yet found the trigger that causes it - sometimes it happens partway through a playthrough, sometimes within a few seconds of starting the game

I assume it must be something to do with the backing texture getting corrupted?

(first reported in https://github.com/not-fl3/macroquad/issues/990#issuecomment-3255411283 by @creepersaur and @tom-sson )