ui/vdagent: call vdagent_disconnect() when agent connection is lost

when the agent connection is lost, the input handler of the mouse
doesn't deactivate, which results in unresponsive mouse events in
VNC windows.

To fix this issue, call vdagent_disconnect() to reset the state
each time the frontend disconncect

Signed-off-by: Guoyi Tu <tugy@chinatelecom.cn>
Signed-off-by: dengpengcheng <dengpc12@chinatelecom.cn>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <71fd5a58fd09f10cdb35f167b2edb5669300116e.1692281173.git.tugy@chinatelecom.cn>

ui/vdagent.c

@@ -870,8 +870,11 @@ static void vdagent_disconnect(VDAgentChardev *vd)
 
 static void vdagent_chr_set_fe_open(struct Chardev *chr, int fe_open)
 {
+    VDAgentChardev *vd = QEMU_VDAGENT_CHARDEV(chr);
+
     if (!fe_open) {
         trace_vdagent_close();
+        vdagent_disconnect(vd);
         /* To reset_serial, we CLOSED our side. Make sure the other end knows we
          * are ready again. */
         qemu_chr_be_event(chr, CHR_EVENT_OPENED);