fix doc block of OC\Preview\Provider::getThumbnail()
fix doc block of OC\Preview\Provider::getThumbnail()

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