Don't assert in wxGenericFileCtrl if there is no selected file.

Don't use the list control item if there is no selection in it.

Closes #16684.

src/generic/filectrlg.cpp

@@ -1064,10 +1064,15 @@ wxFileName wxGenericFileCtrl::DoGetFileName() const
         wxListItem item;
         item.m_itemId = m_list->GetNextItem(-1, wxLIST_NEXT_ALL,
                                             wxLIST_STATE_SELECTED);
+
+        // ... if anything is selected in the list
+        if ( item.m_itemId != wxNOT_FOUND )
+        {
             m_list->GetItem(item);
 
             fn.Assign(m_list->GetDir(), item.m_text);
         }
+    }
     else // user entered the value
     {
         // the path can be either absolute or relative