lib: bt_query_executor_query(): check interruption state before querying

lib: bt_query_executor_query(): check interruption state before querying

This patch makes bt_query_executor_query() check its interruption state
(with bt_query_executor_is_interrupted()) before it calls the user
method. This is just a convenience so that the user does not need to
check bt_query_executor_is_interrupted() for every
bt_query_executor_query() call.

The comment `query-executor.c` explains why the function returns
`BT_QUERY_EXECUTOR_QUERY_STATUS_AGAIN` in that case.

Signed-off-by: Philippe Proulx <eeppeliteloop@gmail.com>
Change-Id: I3bfceed538601d83c1ab627f5241c59f9f2e7c49
Reviewed-on: https://review.lttng.org/c/babeltrace/+/1757
Tested-by: jenkins <jenkins@lttng.org>