Ensure that combobox editor used by wxGrid is tall enough.

Set the rectangle of wxGridCellChoiceEditor to be at least as tall as the best
(i.e. minimal) wxComboBox size because otherwise the control can be unusable.

Closes #13818.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@70693 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775