nbd/client: fix nbd_negotiate_simple_meta_context

nbd/client: fix nbd_negotiate_simple_meta_context

Initialize received variable. Otherwise, is is possible for server to
answer without any contexts, but we will set context_id to something
random (received_id is not initialized too) and return 1, which is
wrong.

To solve it, just initialize received to false. Initialize received_id
too, just to make all possible checkers happy.

Bug was introduced in 78a33ab58782efdb206de14 "nbd: BLOCK_STATUS for
standard get_block_status function: client part" with the whole
function.

Signed-off-by: Vladimir Sementsov-Ogievskiy <[email protected]>
Message-Id: <20180427142002[email protected]>
Reviewed-by: Eric Blake <[email protected]>
CC: [email protected]
Signed-off-by: Eric Blake <[email protected]>