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GH-35684: [Go][Parquet] Fix nil dereference with nil list array (#35690)



### Rationale for this change
If a column to be written to parquet is a list array with only nulls in it, then the child will be empty and potentially have nil buffers. This case isn't checked in the `writeDenseArrow` function, so we blindly attempt to grab the bytes from the buffers which might be nil. 

### What changes are included in this PR?
Adding a check of `leafArr.Len()` at the top of `writeDenseArrow`. If the leaf array's length is > 0 we can be sure that the data buffer is non-nil. So we can just bail if the leaf array is empty, nothing to write.

### Are these changes tested?
Unit test is added.

* Closes: #35684

Authored-by: Matt Topol <zotthewizard@gmail.com>
Signed-off-by: Matt Topol <zotthewizard@gmail.com>