make 'a' and 'b' coefficients atleast_1d array in filtfilt

The following crashes:
import numpy as np
from scipy.signal import filtfilt
x = np.random.randn(100)
y = filtfilt(np.ones(5)/5, 1, x)

The problem is in lines 1931 and 1932 of filfilt function, these lines
should be replaced by:
b = np.atleast_1d(b)
a = np.atleast_1d(a)