Incorrect discrete 'curl' colormap

Looks like something is off when you specify a discrete normalization with the curl colormap.
The code below will produce 4 plots; the first 3 are as expected but the last one demonstrates the issue. Colors are no longer centered around 0 (white).

import matplotlib.pyplot as plt
import cmocean
import numpy as np

data = np.random.normal(loc=0, size=(10, 10))
norm = mpl.colors.TwoSlopeNorm(0, -2, 2)

plt.imshow(data, cmap='cmo.balance', norm=norm)
plt.colorbar()
plt.title('TwoSlopeNorm, Balance (Correct)')

plt.figure()
plt.imshow(data, cmap='cmo.curl', norm=norm)
plt.colorbar()
plt.title('TwoSlopeNorm, Curl (Correct)')

bounds = np.linspace(-2, 2, 21)
norm = mpl.colors.BoundaryNorm(bounds, 256)

plt.figure()
plt.imshow(data, cmap='cmo.balance', norm=norm)
plt.colorbar()
plt.title('BoundaryNorm, Balance (CORRECT)')

plt.figure()
plt.imshow(data, cmap='cmo.curl', norm=norm)
plt.colorbar()
plt.title('BoundaryNorm, Curl (INCORRECT)');

首先使用 matplotlib、cmocean、numpy、TwoSlopeNorm 和 BoundaryNorm 运行 issue 中的四图复现。比较在 BoundaryNorm 下 cmo.balance 和 cmo.curl 的结果，然后检查 curl 颜色映射的设置和相关的归一化行为；完成的标准是离散的 curl 颜色像连续示例一样以 0 为中心。