Fix avro records where array contains nullable array

TCOMP-2119 fix was not complete (not unwrap nullable in all case)

Bug was discovered on connectors-se/stream-json Unit Test; with usage of Array of Array.

Fault code is covered by compopnent-runtime unit test (so, also the fix), but not with the use case that reveals the bug.

Code fix is enough for making connectors-se/stream-json Unit Test working.

(A future work item will be to add a unit test to cover this case)