VALUE OUT OF RANGE error with Import All when mappings changed #832

Originally reported by @cambot in a comment on #291. I have not yet replicated but we should add some defensive coding to fix anyway:

I had a lookup table that shifted spots in the repository. the internal reference pointed to a file that no longer exists. (I can't remember if I did this manually or the module ended up in this state, but I know I was modifying the export paths experimenting to find a folder structure I liked.)

Here is the exception I get:
GetTempFileAndRoutineTS+7^SourceControl.Git.Utils.1