avfilter/af_adelay: remove requirement that at least one delay should be provided

Such requirement is not necessary and code works without it just fine.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -551,7 +551,6 @@ The filter accepts the following option:
 @table @option
 @item delays
 Set list of delays in milliseconds for each channel separated by '|'.
-At least one delay greater than 0 should be provided.
 Unused delays will be silently ignored. If number of given delays is
 smaller than number of channels all remaining channels will not be delayed.
 If you want to delay exact number of samples, append 'S' to number.

libavfilter/af_adelay.c

@@ -171,11 +171,6 @@ static int config_input(AVFilterLink *inlink)
         s->max_delay = FFMAX(s->max_delay, d->delay);
     }
 
-    if (!s->max_delay) {
-        av_log(ctx, AV_LOG_ERROR, "At least one delay >0 must be specified.\n");
-        return AVERROR(EINVAL);
-    }
-
     switch (inlink->format) {
     case AV_SAMPLE_FMT_U8P : s->delay_channel = delay_channel_u8p ; break;
     case AV_SAMPLE_FMT_S16P: s->delay_channel = delay_channel_s16p; break;