Stop logging a CON.ELV entry in the CALPADS log that has both the Old and New values as blank.

We end up with CALPADS logs that look like this.

  TC     FC     DT              OV      NV
CON ELV 8/15/2024           
CON ELV 8/15/2024           
CON ELV 8/15/2024           
CON ELV 8/15/2024           
CON ELV 8/15/2024           
CON ELV 8/15/2024           
CON ELV 8/14/2024       

This is in a similar vein as the issue outlined in this Aeries Idea:
47387978-calpads-log-should-ignore-con-elv