fix multivalue handling

[WolfgangFahl]

https://www.mediawiki.org/wiki/Extension:Page_Forms/Page_Forms_and_templates#arraymap

is used in some templates and leads to follow up issues as per #30

Analyze which templates use the arraymap parser function from the PageForms extension and improve

[WolfgangFahl]

• https://www.openresearch.org/wiki/Template:Event
• https://confident.dbis.rwth-aachen.de/or/index.php?title=Template:Event

{{#ifeq:{{#arraymap:{{{Field|}}}|, |var|[[Category:var]]| }}|||{{#arraymap:{{{Field|}}}|, |var|[[Category:var]]| }}}}
{{#arraymap:{{#show: {{PAGENAME}}| ?Event in series.Field|link=none}}|, |var|[[var]]}}

see https://confident.dbis.rwth-aachen.de/or/index.php?title=Workdocumentation_2021-05-01 how the second line references a non existing property "Field".