Don't re-enter wxComboCtrlBase::HidePopup

Under wxMSW this method is re-entered due to triggering EVT_ACTIVATE when EVT_LEFT_UP is being already handled.
We need to prevent this to avoid generating spurious EVT_TEXT events and raising errors on calling SetFocus().

Closes #18260.

include/wx/combo.h

@@ -455,7 +455,7 @@ public:
     enum
     {
         Hidden       = 0,
-        //Closing      = 1,
+        Closing      = 1,
         Animating    = 2,
         Visible      = 3
     };