Ensure uncompressed ARCs are properly supported

[anjackson]

So, following on from iipc/openwayback#101, the idea is to test support for uncompressed ARCs from here and try to ensure we can check when this goes wrong.

[anjackson]

Working on a branch of our own repo (ukwa@b45ea54) I've found that the

ArchiveReader reader = ARCReaderFactory.get(fPath, is, false);

approach to firing up the reader always fails. This appears to be because the atFirstRecord == false does not get passed down correctly, and consequently the ARCRecord.parseHeaders method always attempts to read three lines (i.e. like the start of an ARC files) rather than just one.

This seems to be clearly wrong, but it is NOT clear that this is the issue underlying the original problem. This always goes wrong (not just for long offsets), and has nothing to do with seek().

[anjackson]

Modifying the UncompressedARCReader to take the atFirstRecord argument and pass it down in the same way as the CompressedARCReader fixes the test.

[johnerikhalse]

This fix worked in our environment. Closing it.