(toggle_subshell): fix possible race condition on SIGWINCH handling.

If a SIGWINCH were handled after setting was_sigwinch to 0 but before
flushing the pipe, the SIGWINCH would be missed.
Fix that using return value of tty_flush_winch().

Thanks Michael Gold <michael@bitplane.org>.

Signed-off-by: Andrew Borodin <aborodin@vmail.ru>

Author: aborodin

src/execute.c

@@ -547,8 +547,7 @@ toggle_subshell (void)
      * Save sigwinch flag that will be reset in mc_refresh() called via update_panels().
      * There is some problem with screen redraw in ncurses-based mc in this situation.
      */
-    was_sigwinch = tty_got_winch ();
-    tty_flush_winch ();
+    was_sigwinch = tty_flush_winch ();
 
 #ifdef ENABLE_SUBSHELL
     if (mc_global.tty.use_subshell)