fix for iconic_taxon filter bug on lifelists

fix for bug described here: https://groups.google.com/forum/#!topic/inaturalist/XO_kkdgPJSA
that was introduced with the dynamic list filters and fixed for checklists here:
https://github.com/inaturalist/inaturalist/commit/39023094c4dfb242df2a0d8a33b37d5481b22852
this is an analogous fix for non-checklists