Bug 1364133 - Part 1. Check whether SplitNode returns error. r=masayuki

When SplitNode returns nullptr, GetAsText causes crash.  So we should check
error before casting by GetAsText.

MozReview-Commit-ID: 8E1OPSRZ2x5

--HG--
extra : rebase_source : 48a067bd080e7a68e9d469c07d3b744508dae91f

editor/libeditor/HTMLStyleEditor.cpp

@@ -287,10 +287,10 @@ HTMLEditor::SetInlinePropertyOnTextNode(Text& aText,
 
   // Do we need to split the text node?
   ErrorResult rv;
-  RefPtr<Text> text = &aText;
+  nsCOMPtr<nsIContent> text = &aText;
   if (uint32_t(aEndOffset) != aText.Length()) {
     // We need to split off back of text node
-    text = SplitNode(aText, aEndOffset, rv)->GetAsText();
+    text = SplitNode(*text, aEndOffset, rv);
     NS_ENSURE_TRUE(!rv.Failed(), rv.StealNSResult());
   }