Fix memory leak in childAt

Delete the interface if it's not returned.

Change-Id: Ia1e1f94d14584ab3af1b89a0baac5d343ffdd1f4
Reviewed-by: Frederik Gladhorn <frederik.gladhorn@digia.com>

src/gui/accessible/qaccessibleobject.cpp

@@ -165,6 +165,8 @@ QAccessibleInterface *QAccessibleObject::childAt(int x, int y) const
         Q_ASSERT(childIface);
         if (childIface->rect().contains(x,y)) {
             return childIface;
+        } else {
+            delete childIface;
         }
     }
     return 0;