`ZoomedScene` animation broken when no updaters present

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```py
class Testing1(ZoomedScene):
def __init__(self, **kwargs):
ZoomedScene.__init__(
self,
zoom_factor=0.3,
zoomed_display_height=4,
zoomed_display_width=4,
image_frame_stroke_width=20,
zoomed_camera_config={
"default_frame_stroke_width": 3,
},
**kwargs
)
def construct(self):
d= Dot()
self.add(d)
imgo =Square().scale(0.3).set_color(RED)
self.add(imgo)
#imgo.add_updater(lambda x: x.become(x)) # COMMENTED OUT
self.activate_zooming(animate=True)
self.play(self.zoomed_camera.frame.animate.shift(0.5 * (LEFT+UP*0.8)))
self.play(self.zoomed_camera.frame.animate.shift(0.5 * (RIGHT+DOWN*2.8)))

```
gives:

https://user-images.githubusercontent.com/44469195/113008172-18e92380-9177-11eb-995f-578aa0a9288c.mp4

However, `imgo.add_updater(lambda x: x.become(x))`in not commented out gives:

https://user-images.githubusercontent.com/44469195/113008314-38804c00-9177-11eb-98eb-7c43979b4e92.mp4

Start by running the provided Testing1 example and inspect the ZoomedScene entry points used by activate_zooming(animate=True) and the subsequent frame shifts. Compare behavior with and without the imgo updater; done means both cases produce the intended zoom animation consistently.

Written by the indexing model from the issue text.