vd_lavc: change VDCTRL_REINIT_VO behavior

This tried to use ctx->pic (last decoded AVFrame) for the frame bounds.
However, if av_frame_unref() on the AVFrame is called, the function will
reset _all_ AVFrame fields, even those which are not involved with
memory management. As result, mpcodecs_config_vo() was called with 0
width/height, which made the function exit early, instead of
reconfiguring the filter chain.

Go back to using mpcodecs_config_vo() directly. (That's what it did
before this VDCTRL was originally introduced; the original reason for
it disappeared.)

video/decode/vd_lavc.c

@@ -773,9 +773,7 @@ static int control(sh_video_t *sh, int cmd, void *arg)
         *(int *)arg = delay;
         return CONTROL_TRUE;
     case VDCTRL_REINIT_VO:
-        if (ctx->vo_initialized)
-            ctx->vo_initialized = false;
-        init_vo(sh, ctx->pic);
+        mpcodecs_config_vo(sh, sh->disp_w, sh->disp_h, ctx->best_csp);
         return true;
     }
     return CONTROL_UNKNOWN;