Cygwin: console: Fix exit code for non-cygwin process.

If non-cygwin process is executed in console, the exit code is not
set correctly. This is because the stub process for non-cygwin app
crashes in fhandler_console::set_disable_master_thread() due to NULL
pointer dereference. This bug was introduced by the commit:
3721a75 ("Cygwin: console: Make the console accessible from
other terminals."), that the pointer cons is accessed before fixing
when it is NULL. This patch fixes the issue.

Fixes: 3721a75 ("Cygwin: console: Make the console accessible from other terminals.")
Reported-by: Johannes Schindelin <Johannes.Schindelin@gmx.de>
Signed-off-by: Takashi Yano <takashi.yano@nifty.ne.jp>

winsup/cygwin/fhandler/console.cc

@@ -4537,16 +4537,16 @@ fhandler_console::need_console_handler ()
 void
 fhandler_console::set_disable_master_thread (bool x, fhandler_console *cons)
 {
-  const _minor_t unit = cons->get_minor ();
-  if (con.disable_master_thread == x)
-    return;
   if (cons == NULL)
     {
       if (cygheap->ctty && cygheap->ctty->get_major () == DEV_CONS_MAJOR)
 	cons = (fhandler_console *) cygheap->ctty;
       else
 	return;
     }
+  const _minor_t unit = cons->get_minor ();
+  if (con.disable_master_thread == x)
+    return;
   cons->acquire_input_mutex (mutex_timeout);
   con.disable_master_thread = x;
   cons->release_input_mutex ();