Evas text textblock: call evas_font_free even on null fonts
A null font set can potentially be stored and passed on. There is no
specific fallback in our codebase to roll-back if something like that
This fixes a case where an entry of a null font was not removed from the
fonts_cache and was leaked to subsequent tests (the null font entry was
not removed from the fonts_cache).
Note that this was only apparent when EFL was built with
--disable-fontconfig, likely due to fontconfig succeeding to always
retrieve some non-null font.