Fix crash after failing to load SP game library

When loading a game in SP, UI_FreeAllSpecies can be called twice without an initialization in between if the SP game library could not be loaded. This results in a double free crash. This commit fixes the issue by resetting some variables after freeing so that calling free again is a no-op.

Author: xycaleth

code/ui/ui_main.cpp

@@ -2432,6 +2432,9 @@ void UI_FreeAllSpecies( void )
 		UI_FreeSpecies(&uiInfo.playerSpecies[i]);
 	}
 	free(uiInfo.playerSpecies);
+	
+	uiInfo.playerSpeciesCount = 0;
+	uiInfo.playerSpecies = NULL;
 }
 
 /*