Point to '--last-rev' when the origin ref cannot be found
Point to '--last-rev' when the origin ref cannot be found

This is usually the result of imports into overlapping paths.

PiperOrigin-RevId: 322222619
Change-Id: Iad58d05045d46de4eb0b7467d3de1a815bb0fdfc

google/copybara,google/copybara,google/copybara