sceFontRebindRenderer had no test. The new one opens a font without a renderer
and checks every return it reports: a null handle and a block with a zero
handle magic give SCE_FONT_ERROR_INVALID_FONT_HANDLE, an unbound font gives
SCE_FONT_ERROR_NOT_BOUND_RENDERER, a bound font gives SCE_FONT_OK (twice), and
the font reports NOT_BOUND_RENDERER again after sceFontUnbindRenderer.
Co-Authored-By: Claude Sonnet 5.5 <[email protected]>
