Don't use mFirstChild when the child count is zero. b=381057 r=aaronleventhal

git-svn-id: svn://10.0.0.236/trunk@226662 18797224-902f-48f8-a5cc-f745e15eee43

mozilla/accessible/src/atk/nsXULTreeAccessibleWrap.cpp

@@ -64,7 +64,7 @@ NS_IMETHODIMP nsXULTreeAccessibleWrap::GetChildCount(PRInt32 *aAccChildCount)
   // by going through DOM structure of XUL tree
   nsAccessible::GetChildCount(aAccChildCount);
 
-  if (*aAccChildCount != eChildCountUninitialized) {
+  if (*aAccChildCount != 0 && *aAccChildCount != eChildCountUninitialized) {
     // add the count of table cell (or tree item) accessibles, which are
     // created and appended by XUL tree accessible implementation
     PRInt32 rowCount, colCount = 1;