Don't set the initial size as minimal size for top level windows.

Don't set the initial size as minimal size for top level windows.

Correct the change of r62814: only call SetMinSize() for non-top-level windows
as the user should be able to resize the top-level ones to be smaller than
their initial size.

This also fixes the GTK+ warning resulting from calling wxTLW::SetMinSize()
from the ctor, before the window is realized.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62817 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775