GH-734: Improve CompositeJdbcConsumer error handling and add unit tests

[Odin-BN]

What's Changed

This PR improves error handling in 'CompositeJdbConsumer' by safely handling null 'ValueVector' and 'ResultSet' values to prevent 'NullPointerException', and return the intended 'JdbcConsumerException'.

How was this tested?

Added two unit tests in 'CompositeJdbcConsumerTest':

• 'testHandlesJdbcConsumerExceptionGracefully' verifies 'ArrowType' is captured if vector is valid, and returns the 'JdbcConsumerException' even though 'ResultSet' is null (which gave another NullPointerException previously).
• 'testJdbcConsumerExceptionWhenArrowTypeIsNull' verifies 'ArrowType' is 'null' and returns the 'JdbcConsumerException'.

All tests pass after the change.

Closes #734

[Odin-BN]

@github-actions please add label: bug-fix

[Odin-BN]

Hi @lidavidm ! Would you mind adding the "bug-fix" label to this PR please?

I thought maybe the github actions bot could add it automatically with a message, as assigning the issue but it seems that not.

Thanks in advance!

[lidavidm]

Yeah, usually I label it when I review - maybe I should adjust it so that it's a reminder to reviewers (I originally thought the PR author could add labels...)

[lidavidm]

I'm not sure this addresses the original bug report, which is about when getType throws when we try to get arrowType. If anything, the right fix is to just get the type directly from the vector, rather than indirecting through getMinorType.