Bug 633240 nsIMIMEService.getTypeFromFile(null) crashes [@ nsExternalHelperAppService::GetTypeFromFile(nsIFile*, nsACString_internal&) ]

r=biesi

--HG--
extra : rebase_source : 7b0903e9907d993251a4dae1615f35399e99ca96

uriloader/exthandler/nsExternalHelperAppService.cpp

@@ -2858,6 +2858,7 @@ NS_IMETHODIMP nsExternalHelperAppService::GetTypeFromURI(nsIURI *aURI, nsACStrin
 
 NS_IMETHODIMP nsExternalHelperAppService::GetTypeFromFile(nsIFile* aFile, nsACString& aContentType)
 {
+  NS_ENSURE_ARG_POINTER(aFile);
   nsresult rv;
   nsCOMPtr<nsIMIMEInfo> info;