tdf#90990 - listbox focus issue post dispose.

Change-Id: I091662fed0ebe121d023a1bed1eda79e6eb5a09e

vcl/source/control/ilstbox.cxx

@@ -2241,10 +2241,10 @@ void ImplListBox::SetNoSelection()
 
 void ImplListBox::GetFocus()
 {
-    if (!maLBWindow || maLBWindow->IsDisposed())
-        return;
-
-    maLBWindow->GrabFocus();
+    if (maLBWindow)
+        maLBWindow->GrabFocus();
+    else
+        Control::GetFocus();
 }
 
 vcl::Window* ImplListBox::GetPreferredKeyInputWindow()