Remove unnecessary filter_ensure_valid_filter() call

user_get_bug_filter() already calls filter_ensure_valid_filter(), we
therefore only need to call it when unserializing the filter from token
Split long line to improve code readability
Fix data type mismatch when filtering by date

This was caused by inconsistent initialization of filter, which was set
to 'on' when checkbox was checked, and FALSE when unchecked. We now set
it to 'off' when unchecked.

Use of ternary operator to simplify code.

Fixes #16516
Fix whitespace