thanks, Anno!
i search aroung PL_rsfp_filters but forget about av_len()
as i see in sources number of array's elements is always (av_len() + 1). so i can use statement like:
if ( (av_len(PL_rsfp_filters) + 1) > 1 )
that is equal to already founded checking:
if ( av_len(PL_rsfp_filters) > 0 )