ctf: decoding: accommodate lttng-crash timestamp quirk

ctf: decoding: accommodate lttng-crash timestamp quirk

See previous commit titled:
  src.ctf.fs: index: accommodate lttng-crash timestamp quirk
for an explanation of the non-compliance of lttng-crash traces.

How this commit fixes the decoding for the affected traces
==========================================================
When about to emit a packet end message, check if the said packet is
affected by the trace-crash non-compliance. If it's the case, omit to
update the default_clock_snapshot to the `timestamp_end` of the packet.

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: If965a424afa160692c2ec148fc8f60d3d9ac1273
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1548
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>