Add missing loading indicator for enabled apps
Add missing loading indicator for enabled apps

* happened when an app gets activated, because the
  new appended HTML doesn't contain the loading
  image
* fixes #15806

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