build.bash: handle missing git tags
build.bash: handle missing git tags

The case of a git repo without any tags used to fail
with:

  fatal: No names found, cannot describe anything.

Now we continue, using "[no_tags_found]" as the
version string.

rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs,rfjakob/gocryptfs