Small bug fixes regarding custom difficulty levels

Fixed issue where if the user typed a number greater than the number he
type right before it when specifing the range, the program would throw
the "n must be positive error" from the class Random

I also added class NumbersAreSameException to the program so that
MathOperator.startGameCustom() can throw it if the user specifies range
numbers that are equal.

Fixed issue where if log.txt already exists there would be a blank line
before "Math Quiz!!!..."