csi/writer: End position of a chunk is using wrong virtual position

[zaeleus]

In noodles-csi, the writer is using the chunk start position instead of the end position when writing chunk_end.

https://github.com/zaeleus/noodles/blob/bd1098699a5a0ed87dab0c3e6c496ae13faa358d/noodles-csi/src/writer.rs#L229

This was discovered while verifying #215.