Handled invalid filters in members event repository

fix https://linear.app/tryghost/issue/SLO-82/query-error-unexpected-character-in-filter-at-char-1

- previously, we weren't handling a parsing error, and just bubbling it
  back up the chain
- this would result in an InternalServerError somewhere, which caused
  500s
- we can handle this, because it's just a bad filter
- this adds handling so we return a 422 upon receiving an invalid filter

ghost/members-api/lib/repositories/EventRepository.js

@@ -777,7 +777,15 @@ module.exports = class EventRepository {
         }
 
         const allowList = ['data.created_at', 'data.member_id', 'data.post_id', 'type', 'id'];
-        const parsed = nql(filter).parse();
+        let parsed;
+        try {
+            parsed = nql(filter).parse();
+        } catch (e) {
+            throw new errors.BadRequestError({
+                message: e.message
+            });
+        }
+
         const keys = getUsedKeys(parsed);
 
         for (const key of keys) {

ghost/members-api/test/unit/lib/repositories/event.test.js

@@ -19,6 +19,12 @@ describe('EventRepository', function () {
             });
         });
 
+        it('throws when using invalid filter', function () {
+            should.throws(() => {
+                eventRepository.getNQLSubset('undefined');
+            }, errors.BadRequestError);
+        });
+
         it('throws when using properties that aren\'t in the allowlist', function () {
             should.throws(() => {
                 eventRepository.getNQLSubset('(types:1)');