Fixing bug 594547, crash downstream from nsTreeContentView::InsertRow(). r=bzbarsky@mit.edu, tnikkel@gmail.com, a=jst@mozilla.org

layout/xul/base/src/tree/src/nsTreeContentView.cpp

@@ -1091,11 +1091,14 @@ nsTreeContentView::ContentInserted(nsIDocument *aDocument,
   }
   else if (childTag == nsGkAtoms::option) {
     PRInt32 parentIndex = FindContent(aContainer);
-    PRInt32 index = 0;
-    GetIndexInSubtree(aContainer, aChild, &index);
-    PRInt32 count = InsertRow(parentIndex, index, aChild);
-    if (mBoxObject)
-      mBoxObject->RowCountChanged(parentIndex + index + 1, count);
+
+    if (parentIndex >= 0) {
+      PRInt32 index = 0;
+      GetIndexInSubtree(aContainer, aChild, &index);
+      PRInt32 count = InsertRow(parentIndex, index, aChild);
+      if (mBoxObject)
+        mBoxObject->RowCountChanged(parentIndex + index + 1, count);
+    }
   }
 }