GitLab

Add some error catches to prevent looping at EOF.
Also give better diagnostics.
Also add tests for these cases.

Fixes #12656.

Change-Id: I1355fc149b71c868e740bfa53de29c25d160777d
Reviewed-on: https://go-review.googlesource.com/14710

Reviewed-by: Andrew Gerrand <adg@golang.org>