webdav: return SPACE_UNKNOWN if server do not support quota
webdav: return SPACE_UNKNOWN if server do not support quota

Signed-off-by: Tigran Mkrtchyan <d922616d71ca96f778c63ea49015b141afa0a2ae@desy.de>

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