fix: avoid invalidating when drawing

[pcansUbi]

Description

Currently in onDraw(), the view is sometimes invalidated. This means it will be infinitely redrawn. You can see the behavior by enabling the "Show screen updates" setting in the Android debug settings.

Attached is two videos, the current 1.1.2 version that does infinite redraw, and the proposed fix that don't redraw unless needed.
redraw-issue.zip

It result in poor performance.

Another side effect is that our instrumented tests will wait for the render thread to finish, and that will never happen, so tests are ending in a timeout.

I also removed two unneeded calls to initTimeline() from showStartLine() and showEndLine() since they are private and only called by initLine() that will call initTimeline() itself.

Thanks for sharing your work on this library.

[vipulasri]

@pcansUbi thanks for raising this concern, I will look into this.

[vipulasri]

@pcansUbi Thanks for pointing out this performance issue.