lavfi/vf_select: remove looping on request_frame().

libavfilter/f_select.c

@@ -379,18 +379,9 @@ static int filter_frame(AVFilterLink *inlink, AVFrame *frame)
 
 static int request_frame(AVFilterLink *outlink)
 {
-    AVFilterContext *ctx = outlink->src;
-    SelectContext *select = ctx->priv;
     AVFilterLink *inlink = outlink->src->inputs[0];
-    int out_no = FF_OUTLINK_IDX(outlink);
-
-    do {
     int ret = ff_request_frame(inlink);
-        if (ret < 0)
     return ret;
-    } while (select->select_out != out_no);
-
-    return 0;
 }
 
 static av_cold void uninit(AVFilterContext *ctx)