Handle null argument for Selection.selectAllChildren()

Source/core/editing/DOMSelection.cpp

Index: Source/core/editing/DOMSelection.cpp
diff --git a/Source/core/editing/DOMSelection.cpp b/Source/core/editing/DOMSelection.cpp
index 25703e256911f5e5673ad5af24a39089b115e0d4..6a8a63ea9014d7162c73f7c3fced15217a6cb5e4 100644
--- a/Source/core/editing/DOMSelection.cpp
+++ b/Source/core/editing/DOMSelection.cpp
@@ -493,7 +493,8 @@ bool DOMSelection::containsNode(const Node* n, bool allowPartial) const
 
 void DOMSelection::selectAllChildren(Node* n, ExceptionState& exceptionState)
 {
-    ASSERT(n);
+    if (!n)
+        return;
 
     // This doesn't (and shouldn't) select text node characters.
     setBaseAndExtent(n, 0, n, n->countChildren(), exceptionState);