Avoid panics when merging custom annotation/labels

[jon-signal]

This checks that the target maps when merging custom annotations/labels are not nil, thereby avoiding panics. It fixes #2226.

[foundationdb-ci]

Result of fdb-kubernetes-operator-pr on Linux CentOS 7

• Commit ID: a6da988
• Duration 4:10:46
• Result: ❌ FAILED
• Error: Error while executing command: if $fail_test; then exit 1; fi. Reason: exit status 1
• Build Log terminal output (available for 30 days)
• Build Workspace zip file of the working directory (available for 30 days)

[jon-signal]

Result: ❌ FAILED

I think this is from an old run, and I've since fixed the issue.

[foundationdb-ci]

Result of fdb-kubernetes-operator-pr on Linux CentOS 7

• Commit ID: e356f5a
• Duration 3:04:18
• Result: ❌ FAILED
• Error: Error while executing command: if $fail_test; then exit 1; fi. Reason: exit status 1
• Build Log terminal output (available for 30 days)
• Build Workspace zip file of the working directory (available for 30 days)

[johscheuer]

LGTM 👍

[johscheuer]

Thanks!

[jon-signal]

Cheers! Thanks for the quick response!