Fix for #17178
Fix for #17178

If no array of arrays is submitted make sure we still keep $sharedUsers
and $sharedGroups as arrays so the rest of the code keeps functioning as
it should.

owncloud/core,andreas-p/nextcloud-server,michaelletzgus/nextcloud-server,bluelml/core,endsguy/server,xx621998xx/server,IljaN/core,lrytz/core,xx621998xx/server,IljaN/core,cernbox/core,whitekiba/server,jbicha/server,whitekiba/server,pollopolea/core,nextcloud/server,Ardinis/server,nextcloud/server,pixelipo/server,andreas-p/nextcloud-server,owncloud/core,phil-davis/core,owncloud/core,pollopolea/core,pollopolea/core,andreas-p/nextcloud-server,xx621998xx/server,endsguy/server,owncloud/core,whitekiba/server,pmattern/server,bluelml/core,pmattern/server,lrytz/core,whitekiba/server,pmattern/server,pixelipo/server,andreas-p/nextcloud-server,owncloud/core,cernbox/core,michaelletzgus/nextcloud-server,lrytz/core,sharidas/core,sharidas/core,jbicha/server,pollopolea/core,Ardinis/server,michaelletzgus/nextcloud-server,IljaN/core,pixelipo/server,sharidas/core,pmattern/server,michaelletzgus/nextcloud-server,jbicha/server,jbicha/server,cernbox/core,sharidas/core,xx621998xx/server,lrytz/core,cernbox/core,endsguy/server,pixelipo/server,nextcloud/server,pollopolea/core,Ardinis/server,jbicha/server,andreas-p/nextcloud-server,IljaN/core,pixelipo/server,endsguy/server,bluelml/core,IljaN/core,whitekiba/server,xx621998xx/server,cernbox/core,bluelml/core,lrytz/core,Ardinis/server,endsguy/server,bluelml/core,sharidas/core,Ardinis/server,pmattern/server,nextcloud/server