src.ctf.fs: query.cpp: change assertions into exceptions

src.ctf.fs: query.cpp: change assertions into exceptions

Signed-off-by: Francis Deslauriers <francis.deslauriers@efficios.com>
Change-Id: I21d5f8950ca8efa78713404a29c36442cba6502a
Reviewed-on: https://review.lttng.org/c/babeltrace/+/8181
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/12273
Tested-by: jenkins <jenkins@lttng.org>
CI-Build: Simon Marchi <simon.marchi@efficios.com>