ValueError raised for certain systems with nyquist

ValueError raised for certain systems with nyquist_response

For certain systems, when "indent_direction" is set to 'none', a ValueError is thrown on

Line 1456 in 71bd731

count = int(np.round(encirclements, 0))

when there is an attempt at casting the number of encirclements to an integer, but the number of encirclements is not a valid number (NaN).

Code to reproduce:

import sympy as smp
from control import tf, nyquist_response
s = tf('s')

tf1 = ((1 + 5/s)/(1 + 0.5/s))**2   # Double-Lag-Compensator

nyquist_response(tf1, warn_encirclements=False, indent_direction='none')