Win32: Update some funcs in FileUtil.cpp for Unicode(and as a result, correctly use directories with Chinese/Russian/etc. in the path).

The saga of converting Win32 to Unicode isn't over: this should fix https://github.com/hrydgard/ppsspp/issues/3456. I tested from a similarly named directory and noticed no issues with this updated code. I tested loading states, saving states, and having Gran Turismo create and load an autosave.