(ITS#8180) back-sock should not return sucess in case of error

[michael@stroeder.com]

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Submission from: (NULL) (84.181.173.53)


back-sock should definitely never return success(0) to the client in case the
external listener returned non-parseable message:

Example trace log:

55913915 => str2entry: "FOOBAR
msgid: 1
code: 49

"
55913915 <= str2entry NULL (parse_line)
55913915 str2entry: entry -1 has no dn
55913915 str2entry(FOOBAR) failed
55913915 sock: fgets failed: Success (0)