[-NSPasteboard dataForType:] returns an autoreleased NSString,
and callings its release method will result in double-free when
the global autorelease pool is released. Use NSAutoreleasePool to
release it properly.

Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Message-Id: <20220614212131.94696-1-akihiko.odaki@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>