Fix setup of namespace 1 URI

[jojastahl]

Fix namespace 1 initialisation problem that was introduced in commit fd08d01.

Fixes #2692

[jpfr]

Looks good!
We should document at which point the ns1 URI is finalized in the server.
What would be required to allow changes later in the lifecycle?

[jojastahl]

We should document at which point the ns1 URI is finalized in the server.

This is as soon as the Namespace Array is read or written via node value read / write services, or UA_Server_addNamespace, UA_Server_getNamespaceByName or UA_Server_run_startup is called.

What would be required to allow changes later in the lifecycle?

I do not know if this should be possible. Currently writing to the namespace array via node value write service actively checks that existing namespaces are not changed. So I'm afraid, that changing a namespace URI later on is an allowed operation as this changes the identification of all nodes referring to its index.

[Pro]

I added some more comments. This can be merged as soon as CI is green