plugins: call bt_current_thread_clear_error() when not propagating error

plugins: call bt_current_thread_clear_error() when not propagating error

Most of the locations where bt_current_thread_clear_error() is called in
this patch need to be replaced with proper error handling, except in
finalization methods which cannot fail. This work will be done by a
subsequent patch.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I10fb2eb98f46e685e6abf563346a2750b46b01d9
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1613
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Simon Marchi <simon.marchi@efficios.com>