CASSANALYTICS-147: BufferingInputStream fails to read last chunk

[lukasz-antoniak]

Fixes CASSANALYTICS-147.

[lukasz-antoniak]

I am not sure how effective the change in BufferingInputStream would affect skip() used during BIG index reading. All integration tests pass though, and I think hereby unit test is just a simulation.

[lukasz-antoniak]

According to below JavaDoc, ranges should be considered inclusive.

/**
 * Asynchronously request bytes for the SSTable file component in the range start-end, and pass on to the StreamConsumer when available.
 * The start-end range is inclusive.
 *
 * @param start    the start of the bytes range
 * @param end      the end of the bytes range
 * @param consumer the StreamConsumer to return the bytes to when the request is complete
 */
void request(long start, long end, StreamConsumer consumer);

[arjunashok]

Seems like FileSystemSource.request() has a workaround (lines 94–99) that was compensating for the old off-by-one in BufferingInputStream.requestMore().
Comment in line 97: "Start-end range is inclusive but on the final request end == length so we need to exclude".

With this fix, end is now at most source.size() - 1, and length equals source.size(), so length <= end is always false.
As a result -

1. the code always takes the increment = 1 path, which happens to produce the correct end - start + 1, so no data corruption, but it's confusing dead code.

2. More importantly, close is never true, so the autoClose path in the finally block never triggers.
   For sequential reads via FileSystemSSTable (non-BTI format, where autoClose = true), the RandomAccessFile handle is never closed after the last chunk, which is a file descriptor leak.

[arjunashok]

Minor: We might want to assert on returnedBuffers.size() == 2 to catch regressions where extra or missing requests are issued