Bult-in tag group update problem 1.5.0p25 -> 1.6.0p27

[tosch (Tobias Schönau)]

@tosch

I found two hosts haven’t set any of the agent tags, fix this and will try the update and cleanup again. This is maybe causing the problem.

This fixed the stack trace problem on the update process. No clue how hosts ended without any agent tag.