ui/cocoa: Do not exit immediately after shutdown

ui/cocoa used to call exit immediately after calling
qemu_system_shutdown_request, which prevents QEMU from actually
perfoming system shutdown. Just sleep forever, and wait QEMU to call
exit and kill the Cocoa thread.

Signed-off-by: Akihiko Odaki <akihiko.odaki@gmail.com>
Message-Id: <20210219111652.20623-1-akihiko.odaki@gmail.com>
Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>

ui/cocoa.m

@@ -1115,7 +1115,13 @@ - (void)applicationWillTerminate:(NSNotification *)aNotification
     COCOA_DEBUG("QemuCocoaAppController: applicationWillTerminate\n");
 
     qemu_system_shutdown_request(SHUTDOWN_CAUSE_HOST_UI);
-    exit(0);
+
+    /*
+     * Sleep here, because returning will cause OSX to kill us
+     * immediately; the QEMU main loop will handle the shutdown
+     * request and terminate the process.
+     */
+    [NSThread sleepForTimeInterval:INFINITY];
 }
 
 - (BOOL)applicationShouldTerminateAfterLastWindowClosed:(NSApplication *)theApplication