Don't access display after i/o error (Bug#19147).

* xterm.c (x_connection_closed): Add third arg ioerror.
If ioerror, set display to 0 (Bug#19147).
(x_error_quitter): Call x_connection_closed with third arg false.
(x_io_error_quitter): Call x_connection_closed with third arg true.

src/xterm.c

@@ -259,7 +259,7 @@ static int x_dispatch_event (XEvent *, Display *);
 #endif
 /* Don't declare this _Noreturn because we want no
    interference with debugging failing X calls.  */
-static void x_connection_closed (Display *, const char *);
+static void x_connection_closed (Display *, const char *, bool);
 static void x_wm_set_window_state (struct frame *, int);
 static void x_wm_set_icon_pixmap (struct frame *, ptrdiff_t);
 static void x_initialize (void);
@@ -8456,7 +8456,7 @@ static char *error_msg;
    the text of an error message that lead to the connection loss.  */
 
 static void
-x_connection_closed (Display *dpy, const char *error_message)
+x_connection_closed (Display *dpy, const char *error_message, bool ioerror)
 {
   struct x_display_info *dpyinfo = x_display_info_for_display (dpy);
   Lisp_Object frame, tail;
@@ -8475,6 +8475,7 @@ x_connection_closed (Display *dpy, const char *error_message)
       dpyinfo->reference_count++;
       dpyinfo->terminal->reference_count++;
     }
+  if (ioerror) dpyinfo->display = 0;
 
   /* First delete frames whose mini-buffers are on frames
      that are on the dead display.  */
@@ -8612,7 +8613,7 @@ x_error_quitter (Display *display, XErrorEvent *event)
   XGetErrorText (display, event->error_code, buf, sizeof (buf));
   sprintf (buf1, "X protocol error: %s on protocol request %d",
 	   buf, event->request_code);
-  x_connection_closed (display, buf1);
+  x_connection_closed (display, buf1, false);
 }
 
 
@@ -8627,7 +8628,7 @@ x_io_error_quitter (Display *display)
 
   snprintf (buf, sizeof buf, "Connection lost to X server `%s'",
 	    DisplayString (display));
-  x_connection_closed (display, buf);
+  x_connection_closed (display, buf, true);
   return 0;
 }