Nil reference in abci.go after new zone onboarding

[joe-bowman]

Summary of Bug

Line 55 of interchainstaking/keeper/abgi.go attempts to access the address of a zone's delegation account, which can for a newly onboarded zone, be nil.

Expected Behaviour

No error thrown if a new zone is encountered.

Version

v1.7.0

Steps to Reproduce

Add guardrails around the query to check whether the account has been initialised yet.

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