winemac: Only update window minimized state when it has changed from what processed events told us it was.

This fixes a problem where windows could spontaneously re-minimize after
being unminimized.  Cocoa would see the window unminimize.  It would queue
a WINDOW_DID_UNMINIMIZE event.  While that event was pending, Wine might do
something which caused set_cocoa_window_properties() to be called and tell
Cocoa to conform itself to the current Win32 state.  The current Win32 state
still had the window minimized, so Cocoa would re-minimize the window.  It
would even discard the WINDOW_DID_UNMINIMIZE event.