XQuartz: xpbproxy: Don't take down the whole server on an IO error

Calls pthread_exit to prevent _XIOError from calling exit()

This fixes http://xquartz.macosforge.org/trac/ticket/421

Signed-off-by: Jeremy Huddleston <jeremyhu@apple.com>
(cherry picked from commit 750d4e82a0)

hw/xquartz/pbproxy/main.m

@@ -75,6 +75,8 @@ static int x_io_error_handler (Display *dpy) {
         exit(EXIT_FAILURE);
 #endif
 
+    /* Prevent _XIOError from calling exit() */
+    pthread_exit(NULL);
     return 0;
 }