client/Client.cc: fix logically dead code in_flush_range()

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>