Bug 1025170 - Selection::Modify should return on failure. r=bz

layout/generic/nsSelection.cpp

@@ -5712,6 +5712,7 @@ Selection::Modify(const nsAString& aAlter, const nsAString& aDirection,
            aGranularity.LowerCaseEqualsLiteral("paragraphboundary") ||
            aGranularity.LowerCaseEqualsLiteral("documentboundary")) {
     aRv.Throw(NS_ERROR_NOT_IMPLEMENTED);
+    return;
   }
   else {
     aRv.Throw(NS_ERROR_DOM_SYNTAX_ERR);