ctf: notif-iter.c: check state on BT_CTF_NOTIF_ITER_MEDIUM_STATUS_EOF

ctf: notif-iter.c: check state on BT_CTF_NOTIF_ITER_MEDIUM_STATUS_EOF

When the notif iter's request_bytes() medium operation returns
BT_CTF_NOTIF_ITER_MEDIUM_STATUS_EOF, make sure that the notif iter
instance is in an expected state. Which states are valid depend on the
metadata (is there a packet size or not, etc.). Return an error from
request_medium_bytes() when the state is incorrect.

This solves streams which should fail but pass, for example when the
data ends within the middle of a packet header field, a packet context
field, or an event.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>