Don't include sys/unistd.h unnecessarily when using MinGW.

This doesn't seem to be needed under Windows where <sys/unistd.h> is just a
wrapper for <io.h> which is already included just below anyhow. And doing this
seems to result in problems with Cygwin MinGW cross-compiler 4.7.3 which seems
to ship with broken version of this file, see the problem described in
http://thread.gmane.org/gmane.comp.lib.wxwidgets.general/80322

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75117 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775
Reset current item in generic virtual wxListCtrl when items count changes.

This ensures that we don't end up with an invalid current item value, which
resulted in the asserts (see
http://thread.gmane.org/gmane.comp.lib.wxwidgets.general/80341) and possibly
worse.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_3_0_BRANCH@75118 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775