vout: use vout_DisplayStarted to check started state

vout_Stop() is stopping the display, but it wasn't accounted the same
way and a decoder video format update could actually try to stop the
display a second time.

include/vlc_vout.h

@@ -126,6 +126,7 @@ vout_CaptionsToDisplay(vout_thread_t *vout, const void *p_cc, size_t i_cc)
  * \param vout the vout to close
  */
 VLC_API void vout_Close(vout_thread_t *vout);
+VLC_API bool vout_DisplayStarted(vout_thread_t *vout);
 
 /**
  * This function will handle a snapshot request.

src/input/resource.c

@@ -370,9 +370,9 @@ static void input_resource_PutVoutLocked(input_resource_t *p_resource,
     assert(vout_rsc != NULL);
 
     if (has_stopped != NULL)
-        *has_stopped = vout_rsc->started;
+        *has_stopped = vout_DisplayStarted(vout_rsc->vout);
 
-    if (vout_rsc->started)
+    if (vout_DisplayStarted(vout_rsc->vout))
     {
         vout_StopDisplay(vout_rsc->vout);
         vout_rsc->started = false;
@@ -500,7 +500,7 @@ vout_thread_t *input_resource_RequestVout(input_resource_t *p_resource,
         return dcfg.vout;
     }
 
-    if (vout_rsc->started)
+    if (vout_DisplayStarted(dcfg.vout))
     {
         assert(cfg->vout != NULL);
         int ret = vout_ChangeSource(dcfg.vout, dcfg.fmt);

src/video_output/video_output.c

@@ -2351,6 +2351,14 @@ static void vout_DisableWindow(vout_thread_sys_t *sys)
     vlc_mutex_unlock(&sys->window_lock);
 }
 
+bool vout_DisplayStarted(vout_thread_t *vout)
+{
+    vout_thread_sys_t *sys = VOUT_THREAD_TO_SYS(vout);
+    assert(!sys->dummy);
+
+    return sys->display != NULL;
+}
+
 void vout_Stop(vout_thread_t *vout)
 {
     vout_thread_sys_t *sys = VOUT_THREAD_TO_SYS(vout);