Fixed a bug with the new feature "Specify number correct" where questions could not be graded.
Fixed a bug with the new feature "Specify number correct" where questions could not be graded.

Summary: The problem was that when "Specify number correct" was checked, the problem could not be graded, because of a faulty if statement logic. I combined the check for the feature with the case that the user does not select the correct number of choices, so now questions with this new feature should be gradeable.

Test Plan:
 - Go to/create a multiple choice, multi-select question and check the box that says "Specify number correct".
 - Go to the preview of the question and select the appropriate number of choices.
 - Click "Check" and verify that the check succeeds (tells you whether you got it wrong or right).

Reviewers: emily

Reviewed By: emily

Subscribers: jared

Differential Revision: https://phabricator.khanacademy.org/D37255

learningequality/perseus,learningequality/perseus,ariabuckles/perseus,ariabuckles/perseus,ariabuckles/perseus,ariabuckles/perseus