Clipping of rate function values in animations cause wiggle not to work properly

Using code from 06/10, I could not get the following simple wiggle scene to render properly:
```
class test(Scene):
def construct(self):
dot = Dot(color=YELLOW)
self.add(dot)
self.play(dot.shift, RIGHT, rate_func=lambda t: wiggle(t,6),run_time=5)
self.wait(1)
```
The movement would occur in one direction as expected but not on the other. After digging into the code, I found the following lines in manimlib/animation/animation.py:
```
def get_sub_alpha(self, alpha, index, num_submobjects):
# TODO, make this more understanable, and/or combine
# its functionality with AnimationGroup's method
# build_animations_with_timings
lag_ratio = self.lag_ratio
full_length = (num_submobjects - 1) * lag_ratio + 1
value = alpha * full_length
lower = index * lag_ratio
return np.clip((value - lower), 0 1) # <---- could this be -1 instead of 0?
```
Since the wiggle function outputs values in the [-1, 1] interval, I fail to see how it's supposed to work with the above clipping in place. While I understand that it's supposed to be a safety net against wild user-provided rate functions, I believe it's better to extend the clipping to the [-1, 1] interval.