Fix QuizTextHandler.makeCorrection() when the correct answer is 0 #132
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makeCorrection() should first check whether the user's answer is exactly
the same as the correct answer. This fixes the issue that the user's
answer would always be marked incorrect if the correct answer was 0,
because the division-by-0 in the relative error calculation would produce
NaN.
For example:
http://bcaffo.github.io/courses/06_StatisticalInference/homework/hw4.html#6
Enter '0' for the answer to #2 and click "Submit". The red 'X' icon would
appear next to the text box. Next click "Show Answer" and "OK" on the
pop-up. The correct answer is 0 and the green checkmark icon is now shown
next to the text box for #2.