Don't un-maximize the window when Iconize(false) is called in wxMSW.

Don't un-maximize the window when Iconize(false) is called in wxMSW.

Calling Iconize(false) on a maximized window restored it to its normal state
instead of doing nothing as expected.

Return immediately from Iconize() if the requested state is already the
current one to avoid it.

Closes #13373.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@68493 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775