Show warning when invalid user was passed
Show warning when invalid user was passed

Sometimes there are bugs that cause setupFS() to be called for
non-existing users. Instead of failing hard and breaking the instance,
this fix simply logs a warning.

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