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 78a33ab5 "nbd: BLOCK_STATUS for
standard get_block_status function: client part" with the whole
function.
Signed-off-by: NVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20180427142002.21930-2-vsementsov@virtuozzo.com>
Reviewed-by: NEric Blake <eblake@redhat.com>
CC: qemu-stable@nongnu.org
Signed-off-by: NEric Blake <eblake@redhat.com>

nbd/client.c

@@ -613,8 +613,8 @@ static int nbd_negotiate_simple_meta_context(QIOChannel *ioc,
 {
     int ret;
     NBDOptionReply reply;
-    uint32_t received_id;
-    bool received;
+    uint32_t received_id = 0;
+    bool received = false;
     uint32_t export_len = strlen(export);
     uint32_t context_len = strlen(context);
     uint32_t data_len = sizeof(export_len) + export_len +