Each upload chunk is buffered in a pool.RW from the global memory pool
but was never closed, so its pages were never returned to the pool.
Close the buffer after each chunk is uploaded and on the read error
path.
A chunk that failed with a retryable error was also retried without
rewinding the buffer, so the retry sent an empty body with the original
Content-Length and Content-Range and failed.
Seek the chunk back to the start inside the pacer closure so each
attempt re-sends it in full.
The FsPutRetry integration test covers the retry of a failed upload
request and checks the buffers are returned to the pool.
Nick Craig-Wood
2f0228029e