validate the generated email address and fall back to localhost.localdomain in case it is not valid
validate the generated email address and fall back to localhost.localdomain in case it is not valid

fixes #1844

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