vo/xcb: fix a memory leak in Open()

Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>
(cherry picked from commit be82d4c1415c9490ecdccdd4bb2b61cd69499365)

modules/video_output/xcb/xvideo.c

@@ -297,10 +297,11 @@ FindFormat (vout_display_t *vd,
 static int Open (vlc_object_t *obj)
 {
     vout_display_t *vd = (vout_display_t *)obj;
-    vout_display_sys_t *p_sys = malloc (sizeof (*p_sys));
+    vout_display_sys_t *p_sys;
 
     if (!var_CreateGetBool (obj, "overlay"))
         return VLC_EGENERIC;
+    p_sys = malloc (sizeof (*p_sys));
     if (p_sys == NULL)
         return VLC_ENOMEM;