Fix a crash when opening two terminal windows and closing the first one.

To reproduce, launch the terminal, open a second window using Ctrl-Shift-N,
go back to the first window, and press Ctrl-D. The terminal's master FD gets
events even after being closed, causing terminal_destroy to be called twice
on the same object.

To fix this, I'm adding a function to stop watching an FD.

clients/terminal.c

@@ -2578,13 +2578,15 @@ terminal_create(struct display *display)
 static void
 terminal_destroy(struct terminal *terminal)
 {
+	display_unwatch_fd(terminal->display, terminal->master);
 	window_destroy(terminal->window);
 	close(terminal->master);
 	wl_list_remove(&terminal->link);
-	free(terminal);
 
 	if (wl_list_empty(&terminal_list))
-		exit(0);
+		display_exit(terminal->display);
+
+	free(terminal);
 }
 
 static void

clients/window.c

@@ -4346,6 +4346,12 @@ display_watch_fd(struct display *display,
 	epoll_ctl(display->epoll_fd, EPOLL_CTL_ADD, fd, &ep);
 }
 
+void
+display_unwatch_fd(struct display *display, int fd)
+{
+	epoll_ctl(display->epoll_fd, EPOLL_CTL_DEL, fd, NULL);
+}
+
 void
 display_run(struct display *display)
 {

clients/window.h

@@ -146,6 +146,9 @@ void
 display_watch_fd(struct display *display,
 		 int fd, uint32_t events, struct task *task);
 
+void
+display_unwatch_fd(struct display *display, int fd);
+
 void
 display_run(struct display *d);