Add one more simple check to speed up the ZigZag Conversion.

[ghost]

https://github.com/haoel/leetcode/blob/4cda31053dcd42e01fb1bb87cf9f09de55f546e8/src/zigZagConversion/zigZagConversion.cpp#L31

if (nRows >= s.length()) return s;

[haoel]

This is a very good finding, I will fix it in my code soon.

Thanks a lot!