Hardening: Remove dangerous characters + Subdirectory Check
Hardening: Remove dangerous characters + Subdirectory Check

If an user is able to create folders in /core/l10n/ he is able to execute arbitrary code. Therefore I've added an `issubdirectory` check and removed all potential dangerous characters from `$lang`.
IljaN/core,cernbox/core,endsguy/server,whitekiba/server,andreas-p/nextcloud-server,xx621998xx/server,Ardinis/server,Ardinis/server,pmattern/server,cernbox/core,jbicha/server,IljaN/core,whitekiba/server,endsguy/server,owncloud/core,sharidas/core,whitekiba/server,lrytz/core,xx621998xx/server,lrytz/core,xx621998xx/server,cernbox/core,endsguy/server,bluelml/core,pollopolea/core,endsguy/server,pollopolea/core,owncloud/core,endsguy/server,jbicha/server,IljaN/core,pollopolea/core,sharidas/core,bluelml/core,pixelipo/server,whitekiba/server,cernbox/core,andreas-p/nextcloud-server,pmattern/server,jbicha/server,lrytz/core,pollopolea/core,jbicha/server,pixelipo/server,pmattern/server,nextcloud/server,phil-davis/core,sharidas/core,Ardinis/server,andreas-p/nextcloud-server,bluelml/core,sharidas/core,pmattern/server,bluelml/core,whitekiba/server,nextcloud/server,owncloud/core,michaelletzgus/nextcloud-server,cernbox/core,sharidas/core,xx621998xx/server,lrytz/core,michaelletzgus/nextcloud-server,Ardinis/server,andreas-p/nextcloud-server,Ardinis/server,owncloud/core,nextcloud/server,IljaN/core,michaelletzgus/nextcloud-server,xx621998xx/server,pixelipo/server,nextcloud/server,IljaN/core,pollopolea/core,owncloud/core,andreas-p/nextcloud-server,pmattern/server,michaelletzgus/nextcloud-server,lrytz/core,pixelipo/server,pixelipo/server,jbicha/server,bluelml/core