Fix the main radius being too small when Re{p/z} small and Im{p/z} large
Fix the main radius being too small when Re{p/z} small and Im{p/z} large

There were some random transfer functions that produced pole and zero
distributions where some of the p/z had a small real and a large
imaginary value which resulted in the main radius being too small.

Corrected this by defining the main radius now as at least 1.5 times
the largest absolute value of the poles and zeros.

StefanRickli/anp