Made vout_display_t::manage() optional.

include/vlc_vout_display.h

@@ -293,7 +293,7 @@ struct vout_display_t {
     /* Control on the module (mandatory) */
     int        (*control)(vout_display_t *, int, va_list);
 
-    /* Manage pending event (mandatory for now) */
+    /* Manage pending event (optional) */
     void       (*manage)(vout_display_t *);
 
     /* Private place holder for the vout_display_t module (optional)

src/video_output/display.c

@@ -161,6 +161,7 @@ static int vout_display_Control(vout_display_t *vd, int query, ...)
 }
 static void vout_display_Manage(vout_display_t *vd)
 {
+    if (vd->manage)
         vd->manage(vd);
 }