Loading questions can cause fatal errors in unfortunate places

This follows on from MDL-62811.

When you load a question (e.g. using question_bank::load_question_data()), this goes via questionlib.php/_tidy_question to call question_bank::get_qtype($question->qtype)->get_question_options($question);

Since that is code in (potenitally third-party) question types plugins, it is risky to assume that it will always work.

At the moment, if an exception is thrown there, then it cases a fatal error - which might be a good thing. It ensures that bugs are found and fixed. On the other hand, it is a bit unrobust. Perhpas we should have a try-catch there, but then we would have to decide what to do to handle the error.