Applied patch [ 637982 ] wxComboBox needs margin

Applied patch [ 637982 ] wxComboBox needs margin

wxComboBox doesn't have a margin between the text and
the dropdown button when the default size is used.
Since wxTextctrl currently returns a rather long minmal
size, this error is only visible if a long text (around
20 chars) is used. This patch introduces a margin
(analog wxSpinctrl).

Otto Wyss

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@18120 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775