Avoid to insert TAB before HTML element

Source/core/editing/InsertTextCommand.cpp

Index: Source/core/editing/InsertTextCommand.cpp
diff --git a/Source/core/editing/InsertTextCommand.cpp b/Source/core/editing/InsertTextCommand.cpp
index 5d3d91513ab86deac1993a282b216d92dea1cce3..0d6e03f61acffe413df8ceb3e5026ca34a2d8f61 100644
--- a/Source/core/editing/InsertTextCommand.cpp
+++ b/Source/core/editing/InsertTextCommand.cpp
@@ -229,6 +229,8 @@ void InsertTextCommand::doApply()
 Position InsertTextCommand::insertTab(const Position& pos)
 {
     Position insertPos = VisiblePosition(pos, DOWNSTREAM).deepEquivalent();
+    if (insertPos.isNull())
+        return pos;
 
     Node* node = insertPos.containerNode();
     unsigned offset = node->isTextNode() ? insertPos.offsetInContainerNode() : 0;