Show error message if config file is not readable
Show error message if config file is not readable

* when the config file is not writable there is a error message shown
* same happens now if the config file is not readable
* fixes #180

nextcloud/server,andreas-p/nextcloud-server,andreas-p/nextcloud-server,pmattern/server,xx621998xx/server,xx621998xx/server,michaelletzgus/nextcloud-server,michaelletzgus/nextcloud-server,endsguy/server,Ardinis/server,nextcloud/server,xx621998xx/server,pixelipo/server,pmattern/server,pixelipo/server,endsguy/server,pixelipo/server,pmattern/server,andreas-p/nextcloud-server,nextcloud/server,xx621998xx/server,Ardinis/server,michaelletzgus/nextcloud-server,endsguy/server,xx621998xx/server,pmattern/server,whitekiba/server,pixelipo/server,whitekiba/server,Ardinis/server,andreas-p/nextcloud-server,Ardinis/server,jbicha/server,whitekiba/server,jbicha/server,endsguy/server,whitekiba/server,endsguy/server,jbicha/server,jbicha/server,Ardinis/server,pmattern/server,jbicha/server,nextcloud/server,andreas-p/nextcloud-server,pixelipo/server,whitekiba/server,michaelletzgus/nextcloud-server