The issue is noticeable at `millisPerPixel` being between ~ 0.5 & 2.0 the size
of `requestAnimationFrame` period. Canvas image update period would be
inconsistent - some would last longer, some less, some would get skipped
altogether.

Introduced in 86574e

This reverts f1a0a88

Fixes joewalnes#57

No behavior changes

Reduce the amount of checks

This changes behavior a bit - when `render(` is passed a canvas different
from `this.canvas`

and when the user calls `render` manually with a custom `time` argument

…der time

It would depend on `scrollBackwards` and `fillStyle` being `undefined` or not.
Depending on this, it would either continue the line up to the edge of the
canvas or leave it at `lastX`. This makes it so that it is always left at
`lastX`.

…ering

…tore()`"

This reverts commit f7b488e.

For some reason in Chromium 95.0.4638.54 (and maybe others) that change
caused `render()` CPU time to grow over time. For me on the
`examples/example1.html` page it would grow from 0.5ms to 50ms over 5 minutes