Fix filter test for multifield custom column

This adds support for "field||field" without spaces.

Change-Id: Ia738d6642d12a188d1629bbdd9701cc8f8bb7a68
Reviewed-on: https://code.wireshark.org/review/5922
Reviewed-by: Michal Labedzki <michal.labedzki@tieto.com>
Tested-by: Michal Labedzki <michal.labedzki@tieto.com>