sdl2::ttf::init incorrectly incorrectly uses the last OS error.

[sprocklem]

init assumes that only OS errors are encountered during initialization, but this is not the case since the underlying FT_Init_FreeType has other error conditions. Instead, init should get the error from SDL_GetError as documented here (TTF_GetError is #defined as SDL_GetError).

To retain backwards compatibility with the current error type, it may be necessary to wrap the error in an Error with ErrorKind::Other.