fix: tags_to_maps/2 invalid tags filtering out

[charmful0x]

small patch fixing hb_maps:get/4 default passing, then filtering out not_found tags instead of passing Opts as possible name/value

[samcamwilliams]

Thanks, but are there any circumstances in which that should actually occur at that point in the code? In this case I guess this is why we didn't see Opts injected into tags anywhere in the system 😄. Perhaps hb_util:ok(hb_maps:find(...)) instead, so that we throw on error?