Server timezone offset is incorrect

[Stig Arne Bye]

I've discovered a bug in the server timezone offset settings.

The following table show my test results when trying to use different timezone offsets in FileZilla server preferences (Server Administration - Advanced tab).

Table columns
-------------
Local time:     Local computer time.
Setting:        Server timezone offset setting in FZ preferences.
Server time:    Server time shown AFTER adjusting timezone offset.
Actual offset:  The actual timezone offset using current setting.

                                      Actual
  Local time   Setting   Server time  offset
  ----------   -------   -----------  -------
   [...]
   12:00:00      -5 h     06:00:00      -6 h
   12:00:00      -4 h     07:00:00      -5 h
   12:00:00      -3 h     08:00:00      -4 h
   12:00:00      -2 h     09:00:00      -3 h
   12:00:00      -1 h     10:00:00      -2 h
   12:00:00       0 h     11:00:00      -1 h
   12:00:00      +1 h     13:00:00      +1 h
   12:00:00      +2 h     13:00:00      +1 h
   12:00:00      +3 h     14:00:00      +2 h
   12:00:00      +4 h     15:00:00      +3 h
   12:00:00      +5 h     16:00:00      +4 h
   [...]

As seen from the above, when the offset is set to "0", the server time is shown as one hour behind, and using either "+1" or "+2" will both show the server time as one hour ahead...

This bug is present in FileZilla 3.1.6, but was also noticed in previous versions...!