vnc: fix possible uninitialized removals

Some VncState values are not initialized before the Websocket handshake.
If it fails QEMU segfaults during the cleanup. To prevent this behavior
intialization checks are added.

Signed-off-by: Tim Hardeck <thardeck@suse.de>
Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>
diff --git a/ui/vnc.c b/ui/vnc.c
index ee08894..ff4e2ae 100644
--- a/ui/vnc.c
+++ b/ui/vnc.c
@@ -1053,20 +1053,24 @@
     audio_del(vs);
     vnc_release_modifiers(vs);
 
-    QTAILQ_REMOVE(&vs->vd->clients, vs, next);
+    if (vs->initialized) {
+        QTAILQ_REMOVE(&vs->vd->clients, vs, next);
+        qemu_remove_mouse_mode_change_notifier(&vs->mouse_mode_notifier);
+    }
 
     if (QTAILQ_EMPTY(&vs->vd->clients)) {
         dcl->idle = 1;
     }
 
-    qemu_remove_mouse_mode_change_notifier(&vs->mouse_mode_notifier);
     vnc_remove_timer(vs->vd);
     if (vs->vd->lock_key_sync)
         qemu_remove_led_event_handler(vs->led);
     vnc_unlock_output(vs);
 
     qemu_mutex_destroy(&vs->output_mutex);
-    qemu_bh_delete(vs->bh);
+    if (vs->bh != NULL) {
+        qemu_bh_delete(vs->bh);
+    }
     buffer_free(&vs->jobs_buffer);
 
     for (i = 0; i < VNC_STAT_ROWS; ++i) {
@@ -2749,6 +2753,7 @@
 
 void vnc_init_state(VncState *vs)
 {
+    vs->initialized = true;
     VncDisplay *vd = vs->vd;
 
     vs->ds = vd->ds;
diff --git a/ui/vnc.h b/ui/vnc.h
index f93c89a..45d7686 100644
--- a/ui/vnc.h
+++ b/ui/vnc.h
@@ -306,6 +306,7 @@
     QEMUPutLEDEntry *led;
 
     bool abort;
+    bool initialized;
     QemuMutex output_mutex;
     QEMUBH *bh;
     Buffer jobs_buffer;