Bug 633232 nsIMIMEService.getTypeFromURI(null) crashes [@ nsExternalHelperAppService::GetTypeFromURI(nsIURI*, nsACString_internal&) ]

r=biesi

--HG--
extra : rebase_source : a84063964425ac512a1daafcaaa4619b0200eaa6

uriloader/exthandler/nsExternalHelperAppService.cpp

@@ -2800,6 +2800,7 @@ NS_IMETHODIMP nsExternalHelperAppService::GetPrimaryExtension(const nsACString&
 
 NS_IMETHODIMP nsExternalHelperAppService::GetTypeFromURI(nsIURI *aURI, nsACString& aContentType) 
 {
+  NS_ENSURE_ARG_POINTER(aURI);
   nsresult rv = NS_ERROR_NOT_AVAILABLE;
   aContentType.Truncate();