bt2: require msg for _OverflowError in _handle_func_status

bt2: require msg for _OverflowError in _handle_func_status

Pyright says:

    /home/smarchi/src/babeltrace/src/bindings/python/bt2/bt2/utils.py:160:19 - error: Invalid exception class or object
    Constructor for exception type "type[_OverflowError]" requires one or more arguments (reportGeneralTypeIssues)

That's true, _OverflowError has bt2_error._Error as a base, which
requires a message.  Change _handle_func_status to assert that a msg was
provided when handling that case.

Change-Id: I961c336cf53ce13e5f4241728e1131cccb77efcf
Signed-off-by: Simon Marchi <simon.marchi@efficios.com>
Reviewed-on: https://review.lttng.org/c/babeltrace/+/11297
Tested-by: jenkins <jenkins@lttng.org>
Reviewed-by: Philippe Proulx <eeppeliteloop@gmail.com>