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GH-39309: [Go][Parquet] handle nil bitWriter for DeltaBinaryPacked (#39347)



### Rationale for this change
If using the DeltaBinaryPacked encoding, we end up with a nil pointer dereference if we end up with an empty column.

### What changes are included in this PR?
Add a nil check in `EstimatedDataEncodedSize` for the base `deltaBitPackEncoder`. This should only ever occur if we have an empty column with this encoding when closing a row group.

### Are these changes tested?
Yes a unit test was added to verify the fix.

* Closes: #39309

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