fixes #1991

[bena-nasa]

This fixes issue #1991
The problem was that I was defining the file reference date relative to the application start time of the clock, this is fine for non-climatological handling of data.
But for climatological handling (where you must provide the valid_range) it is not.

I was being sloppy and using the year from the valid range to set the reference date, but I really needed to examine full time for the start of the valid_range and correlate that to the file_template to determine the appropriate file reference time

This was only apparent when the application ran for extended times when you crossed a year and it had to update the brackets within a single execution.

Description

Related Issue

Motivation and Context

How Has This Been Tested?

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Trivial change (affects only documentation or cleanup)

Checklist:

• I have tested this change with a run of GEOSgcm (if non-trivial)
• I have added one of the required labels (0 diff, 0 diff trivial, 0 diff structural, non 0-diff)
• I have updated the CHANGELOG.md accordingly following the style of Keep a Changelog

[mathomp4]

@bena-nasa I borrowed this PR to get it ready for a release once merged.

Also, did you do a run of "normal" GEOS to make sure that is all zero-diff?