Bug 1076910 - Add some error checks to gfxUtils::EncodeSourceSurface. r=Bas

gfx/thebes/gfxUtils.cpp

@@ -1184,6 +1184,8 @@ gfxUtils::EncodeSourceSurface(SourceSurface* aSurface,
       }
     }
   }
+  NS_ENSURE_SUCCESS(rv, rv);
+  NS_ENSURE_TRUE(!imgData.empty(), NS_ERROR_FAILURE);
 
   if (aBinaryOrData == eBinaryEncode) {
     if (aFile) {