ocis-glauth won't start with GLAUTH_BACKEND_DATASTORE=owncloud

[pmaier1]

When trying to create a hybrid/bridge setup with oC 10 and OCIS beta5 single binary to authenticate local oC 10 users against ocis-konnectd using OIDC you have to tell ocis-glauth to use the oC10 graphapi backend datastore using GLAUTH_BACKEND_DATASTORE=owncloud, among others.

Steps to reproduce
Launch the beta5 single binary with GLAUTH_BACKEND_DATASTORE=owncloud ./ocis-1.0.0beta5-linux-amd64 server

Expected behavior
OCIS starts all services and ocis-glauth can access the oC 10 user backend via graphapi if the environment is properly configured.

Actual behavior
OCIS starts all services but ocis-glauth won't start and loops with

2020-06-09T19:47:10+02:00 INF Written ldap.key service=glauth
panic: runtime error: index out of range [0] with length 0

goroutine 1 [running]:
github.com/glauth/glauth/pkg/handler.NewOwnCloudHandler(0xc000d63448, 0x2, 0x2, 0x291c5c0, 0xc00154be00)
	/srv/app/pkg/mod/github.com/glauth/glauth@v1.1.3-0.20200228160118-2d4f5d547682/pkg/handler/owncloud.go:316 +0x217
github.com/glauth/glauth/pkg/server.NewServer(0xc000d636f0, 0x2, 0x2, 0x8, 0x28db7a0, 0xc0015ae640)
	/srv/app/pkg/mod/github.com/glauth/glauth@v1.1.3-0.20200228160118-2d4f5d547682/pkg/server/server.go:50 +0x2b6
github.com/owncloud/ocis-glauth/pkg/command.Server.func2(0xc00154bd00, 0x0, 0x0)
	/srv/app/pkg/mod/github.com/owncloud/ocis-glauth@v0.4.0/pkg/command/server.go:257 +0x724
github.com/micro/cli/v2.HandleAction(0x201b8e0, 0xc0015ae630, 0xc00154bd00, 0x0, 0xc000d38d70)
	/srv/app/pkg/mod/github.com/micro/cli/v2@v2.1.2-0.20200203150404-894195727d9c/app.go:540 +0x119
github.com/owncloud/ocis/pkg/command.GLAuthCommand.func1(0xc00154bd00, 0x18, 0x30)
	/drone/src/pkg/command/glauth.go:22 +0x9d
github.com/micro/cli/v2.(*Command).Run(0xc0000b9200, 0xc00154b6c0, 0x0, 0x0)
	/srv/app/pkg/mod/github.com/micro/cli/v2@v2.1.2-0.20200203150404-894195727d9c/command.go:161 +0x4b9
github.com/micro/cli/v2.(*App).RunContext(0xc000092480, 0x290db60, 0xc000042198, 0xc00000e080, 0x2, 0x2, 0x0, 0x0)
	/srv/app/pkg/mod/github.com/micro/cli/v2@v2.1.2-0.20200203150404-894195727d9c/app.go:303 +0x790
github.com/micro/cli/v2.(*App).Run(...)
	/srv/app/pkg/mod/github.com/micro/cli/v2@v2.1.2-0.20200203150404-894195727d9c/app.go:210
github.com/owncloud/ocis/pkg/command.Execute(0x3d180, 0xc0000480b8)
	/drone/src/pkg/command/root.go:53 +0xa9c
main.main()
	/drone/src/cmd/ocis/main.go:10 +0x22

@butonic