Blender Git Loki

Fix last part of T38244: memory leak when scaling any panel

Issue is not noticeable with default font, but i18n one can use more than 500Mo of ram when cached in undreds of different sizes.

Campbell had already done most of the work in rBa780e7f3f09f and rB6b283f116829, just had to call BLF_cache_clear() in _exit funcs of VIEW2D_zoom & co operators.