Added original error to thrown error in mega code

- the original error is not propagated up with the error we throw, so it
  can sometimes be difficult to see what's going on down the line

core/server/services/mega/mega.js

@@ -204,6 +204,7 @@ async function handleUnsubscribeRequest(req) {
         return memberModel.toJSON();
     } catch (err) {
         throw new errors.InternalServerError({
+            err,
             message: 'Failed to unsubscribe member'
         });
     }