Show 404 page when accessing empty share URL
Show 404 page when accessing empty share URL

Testplan:
- [ ] Without: Accessing `public.php?service=files&t=` throws an exception
- [ ] With: No exception thrown and 404 page displayed.

Fixes https://github.com/owncloud/core/issues/14231

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