Ensure hard-coded date ranges are preserved in smart groups

[eileenmcnaughton]

See https://lab.civicrm.org/dev/core/issues/396

Overview

Due to a regression introduced by #11486, smart groups based on manually entered date ranges fail to properly filter by the date ranges when executed.

Before

If you create a smart group based on a search using one of several specially identified date fields (including event participant registration date) and you manually specify a date range instead of selecting a pre-chosen range, then your smart group will be properly saved, but the date range will be ignored when the saved search is executed.

After

Smart groups based on manually selected date ranges properly select the right contacts based on the date ranges entered.

Technical Details

Prior to the fix, CiviCRM issued an undefined index error.

Comments

This is a reviewer's commit. I reviewed @jmcclelland patch & decided

1. it works
2. the issue is on save rather than on load so groups created while this is broken will be incorrect. I think we should consider a 5.6.1 drop @seamuslee001 @totten - getting this into the rc as a first step

[civibot]

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[eileenmcnaughton]

Original pr #12831

[eileenmcnaughton]

Mergins as this is a reviewer's commit