[Cin] Extend the life of still images on the timeline.

[Phyllis Smith]

Fix has been checked into GIT already.  Thanks again to Andrea for finding
this and testing too.  gg/Phyllis

It seems to me that the trim functionalities (buttons 1 or 2 or 3)
> always lead to a mute edit.
> Note: edits are still images and not video; with video no problems.
>
>
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