DiscScrubber: only close the file if it was successfully opened, fixes crash if you try to compress a wii game set to readonly

git-svn-id: https://dolphin-emu.googlecode.com/svn/trunk@3626 8ced0084-cf51-0410-be5f-012b33b47a6e

Source/Core/DiscIO/Src/DiscScrubber.cpp

@@ -195,7 +195,7 @@ bool Scrub(const char* filename, CompressCB callback, void* arg)
 			ERROR_LOG(DISCIO, "Really weird - failed to mark scrubbed disk as scrubbed :s");
 
 cleanup:
-	fclose(pFile);
+	if (pFile) fclose(pFile);
 	delete m_Sector1;
 	delete m_FreeTable;