add "1e-6" to avoid [RuntimWarning: divide by zero encountered in divide or cast]

[XavierJiezou]

t_b = np.maximum((self._A[0] - HazeImg[:, :, 0].astype(float)) / (self._A[0] - self.C0 + 1e-6),
                 (HazeImg[:, :, 0].astype(float) - self._A[0]) / (self.C1 - self._A[0] + 1e-6))
t_g = np.maximum((self._A[1] - HazeImg[:, :, 1].astype(float)) / (self._A[1] - self.C0 + 1e-6),
                 (HazeImg[:, :, 1].astype(float) - self._A[1]) / (self.C1 - self._A[1] + 1e-6))
t_r = np.maximum((self._A[2] - HazeImg[:, :, 2].astype(float)) / (self._A[2] - self.C0 + 1e-6),
                 (HazeImg[:, :, 2].astype(float) - self._A[2]) / (self.C1 - self._A[2] + 1e-6))