Propagate error from packet_seek in case of truncated packet

Report the error all the way up allowing users/scripts to perform error
detection and act on it.

Print to stderr the truncated packet information for easier
identification.

Introduce bt_packet_seek_error enum for specific error handling.

Use the ERANGE errno for error propagation inside bt_iter_next and
ctf_read_event.

Signed-off-by: Jonathan Rajotte <jonathan.rajotte-julien@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>