Bug 626472 part 1 - Define nsnull as nullptr where available; r=ehsan

parser/html/nsHtml5HtmlAttributes.cpp

@@ -116,7 +116,7 @@ nsHtml5HtmlAttributes::getURI(PRInt32 index)
   if (index < length && index >= 0) {
     return names[index]->getUri(mode);
   } else {
-    return nsnull;
+    return 0;
   }
 }