Bug 744464: Fix incorrect bounds-check of unsigned value in nsPlainTextSerializer::AppendElementEnd. r=smaug

content/base/src/nsPlainTextSerializer.cpp

@@ -410,8 +410,9 @@ nsPlainTextSerializer::AppendElementEnd(Element* aElement,
   mOutputString = nsnull;
 
   if (id == nsGkAtoms::head) {
+    NS_ASSERTION(mHeadLevel != 0,
+                 "mHeadLevel being decremented below 0");
     --mHeadLevel;
-    NS_ASSERTION(mHeadLevel >= 0, "mHeadLevel < 0");
   }
 
   return rv;