Fix framebuffer artifacts on zoom and screen change

Attempts to fix #9348 by forcing the framebuffer to skip what it's doing every time the active window or the zoom level changes.

By virtue of being in the same file, also contains a fix for the "strcmpi" error on Windows CodeBlocks compilers. Would that be a problem?
Please fix the style here, and compare fontscalebuffer to 0 instead of NULL.