Work around impossibility to use wxCombobox in wxGrid in wxOSX.

Open the combobox when the editor is initially shown, this somehow ensures
that the combobox selection is taken into account when it is closed while
without this the selection is simply completely ignored.

This is just a hack but at least it allows to use wxGridCellChoiceEditor under
wxOSX which was previously impossible at all.

Closes #12644.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69950 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/grideditors.cpp

@@ -1445,6 +1445,14 @@ void wxGridCellChoiceEditor::BeginEdit(int row, int col, wxGrid* grid)
 
     Combo()->SetFocus();
 
+#ifdef __WXOSX_COCOA__
+    // This is a work around for the combobox being simply dismissed when a
+    // choice is made in it under OS X. The bug is almost certainly due to a
+    // problem in focus events generation logic but it's not obvious to fix and
+    // for now this at least allows to use wxGrid.
+    Combo()->Popup();
+#endif
+
     if (evtHandler)
     {
         // When dropping down the menu, a kill focus event