Bug #38374 --> make sure the temp file we are saving the file to is unqiue by calling make unique.

This call will be replaced by createUnique once that gets checked in. I also need to fix the temp file
name I use as well.
r=sspitzer

uriloader/exthandler/nsExternalHelperAppService.cpp

@@ -452,6 +452,7 @@ NS_IMETHODIMP nsExternalAppHandler::OnStartRequest(nsIChannel * aChannel, nsISup
 #endif
 
   mTempFile->Append(tempLeafName); // make this file unique!!!
+  mTempFile->MakeUnique(nsnull);
 
   nsCOMPtr<nsIFileChannel> mFileChannel = do_CreateInstance(NS_LOCALFILECHANNEL_PROGID);
   if (mFileChannel)