added a for loop to deal with the first chunk problem

The only way that I could think of to deal with the problem where the uniform values fall in the first chunk of area (and thus the formula in the paper cannot be used since z_0 could be negative infinity for lower unbounded domains) was to subtract from z_1. I looked briefly in Jeff's code and seems like that is what is happening there.

Without writing a huge for loop for the whole thing, I am currently still using the vectorized operations and then after that I go back to the sample (where NaN's are produced) and correct for those values in a for loop. My hope is that this for loop will be short for large hulls with many chunks since the uniform values would have to be very small to fall under the first chunk of area.