Fix data type mismatch when filtering by date

Follow-up on commit 1a417b123b1dbea702c3b55ff4e83bc8b8fb5545 which did
not cover all possible cases for the error.

We now consistently store the 'filter by date' property as a boolean,
and rely on gpc_string_to_bool() to ensure any string we get (e.g. 1,
'on', 'true') is properly converted to boolean before comparing. We
therefore no longer need the ternary operator in view_all_set.php. We
use 'on'/'off' when encoding the filter only.

Fixes 0016516