VAAPI vout: release picture itself when refcount reaches 0

The PictureRelease function is being overriden by the vaapi_vout module, but
forgot to release the associated picture when refcount reached zero. This results
in a memory leak for the pictures.

The memleak is solved by this patch.

modules/video_output/vaapi/common.c

@@ -180,10 +180,11 @@ static void PictureUnlock(picture_t *picture)
 /* PictureRelease is called when the picture pool is destroyed. */
 static void PictureRelease(picture_t *picture)
 {
-    if (picture->i_refcount > 0)
-        picture->i_refcount--;
-
     picture->p_sys = NULL;
+    if (--picture->i_refcount > 0)
+        return;
+
+    picture_Delete(picture);
 }
 
 /**
@@ -282,7 +283,7 @@ error:
             vlc_va_surface_t *surface = (vlc_va_surface_t *) pic->p_sys;
             vlc_va_conn_ReleaseSurface(va, surface);
         }
-        picture_Release(pic);
+        picture_Delete(pic);
     }
     free(pic_array);
     va->unlock();