libmagic 5.18

Also includes a patch concerning bugs (fixed upstream already):
  - http://bugs.gw.com/view.php?id=338
  - http://bugs.gw.com/view.php?id=341
  - http://bugs.gw.com/view.php?id=342
libmagic: update 5.18 bottle.

Closes #28060.

Signed-off-by: Mike McQuaid <mike@mikemcquaid.com>