BUG/MAJOR: checks: break infinite loops when tcp-checks starts with comment

BUG/MAJOR: checks: break infinite loops when tcp-checks starts with comment

If a tcp-check sequence starts with "comment", then the action is not
matched in the while() loop and the pointer doesn't advance so we face
an endless loop. It is normally detected early except in the case where
very slow checks are performed causing it to trigger after the admin stops
watching.

This bug is 1.6-only and very recent so it didn't have the time to affect
anyone.