client/Client.cc: fix/silence "logically dead code" CID-Error

Fix handling of 'safe' and the conditions after calling file_flush().

CID 1019548 (#1 of 1): Logically dead code (DEADCODE)
  dead_error_begin: Execution cannot reach this statement "flock.Unlock();"

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>
Merge pull request #291 from dalgaaf/wip-da-CID-1019548

client/Client.cc: fix/silence "logically dead code" CID-Error

Even money that this satisfies the coverity gods...

Reviewed-by: Sage Weil <sage@inktank.com>