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.