after 7f8b62bc0b, its move operator and ctor broke. That potentially
leads to error because data_consume_context dtor moves sstable ref
to continuation when waiting for in-flight reads from input stream.
Otherwise, sstable can be destroyed meanwhile and file descriptor
would be invalid, leading to EBADF.
Fixes#3020.
Signed-off-by: Raphael S. Carvalho <raphaelsc@scylladb.com>
Message-Id: <20171129014917.11841-1-raphaelsc@scylladb.com>