All segments from time zero are reloaded when switching track

Created by: davemevans

https://github.com/Dash-Industry-Forum/dash.js/pull/1242 seems to have caused a regression when switching tracks while fixing multiperiod.

This is because when a new StreamProcessor is created, its currentTime is no longer set which causes the scheduler to start from zero.

This was reported on another ticket - I've copied and pasted the detail below:

@esteban-dosztal wrote:

having an issue that seems related to this. I wrote an audio language selector, ad it works fine, but when I select a different language, I see in Chrome Dev Tools network panel that Dash.js starts to load all the previous audio fragments fragments, i.e., let's say I have to audio languages, english and spanish, and I have advanced in the reproduction, so my current english audio fragment is 250; then I select to change to spanish audio, and Dash starts to load spanish audio fragments from fragment 1. I'm calling this.mediaPlayer_.setTrackSwitchModeFor('audio', 'neverReplace'); before MediaPlayer.attachSource, but it didn't change anything. ¿Am I doing something wrong, or it is a bug in Dash.js? I'm using version 2.1.1.