RcodeZero driver: error when adding a record where already a record with another type exists

[MikeAT]

Summary

The RcodeZero driver generated broken API-Requests when adding records with different type (eg. adding an AAAA record to an existing A record).

Detailed Information

Adding a records to a zone where the same label with a different type already exists leads to brokenAPI requests.
PR #2038 fixes this