Agreements: Display the earliest Start Date when an agreement period is not current

When an agreement has no active period (i.e. the most recent "End date" is in the past) the earliest period start date should display as the "Start date" should display in the agreement preview pane.

Currently the End date for the most recent agreement period is displayed but the corresponding earliest Start date is not.

Screenshot showing the values in the edit pane:

Screenshot showing the resulting preview pane.

This is a simple example with a single period, but if there were multiple periods the earliest start date and the latest end dates would come from different periods