fix a tricky little bug in go generate
fix a tricky little bug in go generate

Without this, vanadium-go-generate fails to correctly clean up and can even
blow away local changes (stashes them but does not correctly unstash them).

Change-Id: I21e8e47d42b4fe2f7778fd4351ea328ec70637e6

vanadium/go.devtools,vanadium/go.devtools,vanadium/go.devtools