BUG/MINOR: checks: return correct error code for srv_parse_agent_check

In srv_parse_agent_check the error code is not returned in case
something goes wrong. The value 0 is always return.

Additionally, there's a small cleanup of unreachable returns that in
most checks are not present either and removed in two places they were
present. This makes the code consistent across the different checks.
1 file changed