sdl: fixed recent bug i introduced that prevented loading savestates 0-9

src/state.cpp

@@ -917,7 +917,7 @@ void FCEUI_LoadState(const char *fname)
 	{
 		FCEUI_MakeBackupMovie(false);	//Backup the movie before the contents get altered, but do not display messages						  
 	}
-	if (!file_exists(fname))
+	if (!file_exists(fname) && fname != NULL)
 	{
 		loadStateFailed = 1;
 		return; // state doesn't exist; exit cleanly