Image resizing is erratic on Android

When viewing images in chat on the Keybase Android client, resizing does not work properly.

Symptoms
- The images do not zoom in consistently (two-finger pinch gesture)
- When viewing an image that was downloaded before, it shows up fully zoomed in
- It's between hard and impossible to zoom out again
- Trying to pan a half-zoomed image (one-finger gesture) often also zooms it more
- There is a noticeable preference to zoom in at any occasion and not zoom back out again

Overall, viewing images is not a pleasurable experience at all. :)

I'm running version 5.2.0-20200129, and my Phone's screen resolution is 1620x1080, if that makes any difference. The zooming glitch has been around since as long as I can remember, i.e. since the early days of the Android client. It's definitely not a regression.

If there is anything else I can share in order to debug this, I'm happy to assist.

No file, test, or entry point is named. Reproduce the issue in the Android client with downloaded and newly viewed images, then trace the image viewer's pinch and pan gesture handling; done means zooming and panning behave consistently in both cases.

Written by the indexing model from the issue text.