Bug 1028522 - Prevent ImageEncoder::ExtractDataInternal from acting on an empty surface. r=gw280

content/canvas/src/ImageEncoder.cpp

@@ -263,6 +263,10 @@ ImageEncoder::ExtractDataInternal(const nsAString& aType,
                                   nsIInputStream** aStream,
                                   imgIEncoder* aEncoder)
 {
+  if (aSize.IsEmpty()) {
+    return NS_ERROR_INVALID_ARG;
+  }
+
   nsCOMPtr<nsIInputStream> imgStream;
 
   // get image bytes