Fix: segmentation fault with multi-trace having non-correlated clocks

Fix: segmentation fault with multi-trace having non-correlated clocks

This bugfix is extracted from commit

commit 61cf588beae752e5ddfc60b6b5310f769ac9e852
Author: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Date:   Tue Feb 9 13:27:24 2016 -0500

    Handle negative time and offset from Epoch

Which was fixing this issue, amongst other things.

[ This fix should be applied to Babeltrace stable 1.3 and 1.4 only. ]

[ This v2 patch removes error checking that was introduced in v1. Since
  the callees don't distinguish between -ENOENT and -EINVAL errors,
  we don't know if we need to error out or not. Keep the original
  1.x behavior (no error checking). ]

Fixes: #790
Signed-off-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Signed-off-by: Jérémie Galarneau <jeremie.galarneau@efficios.com>