Changing the font in front of nk_begin() segaults

Changing the font to anything else than the default one, in front of nk_begin(), segfaults nuklear.
Naming a window with glyphs, which require another font, other than the very first baked font, is thus impossible.

I split eastern and western languages into different fonts, because the eastern languages require a bigger font to be legible.
Because of this behavior, I cannot name Windows in eastern languages. The workaround requires me to create a "Window naming font", which has to be the very first font created.

Start at nk_begin() and the font setup/order described in the report, then reproduce the crash by selecting a non-default font before beginning a window. Done means window names using glyphs from a non-first font no longer segfault, including the reported eastern-language case.

Written by the indexing model from the issue text.