Add test reproducing IO-639 (empty first line handling)

[Reranko05]

This PR adds a unit test that reproduces IO-639.

ReversedLinesFileReader does not return an empty first line when a file
starts with a line separator (for example, a newline-only file). The
added test demonstrates the current behavior and documents the expected
result.

A fix appears to require deeper refactoring of ReversedLinesFileReader,
so this PR is limited to test coverage only.

[garydgregory]

Hello @Reranko05
-1: This PR fails the build and this class already contains the disabled test testEmptyFirstLine(int). An additional test would only be needed if a fix was included that required coverage not already provided.

[Reranko05]

Thanks for clarification, Gary.
Understood, I missed that testEmptyFirstLine(int) already exists in a disabled state.
Since this PR does not include a fix and the coverage already exists, I agree that this additional test case is unnecessary.
I will close the PR accordingly. Thanks for the review and guidance.