fix(ios): keep subtitle selection on foreground

[Myst1024]

Summary

• When playing an m3u8 file with embedded subtitle tracks, the user's subtitle selections are wiped out whenever the player is foregrounded. This PR prevents that scenario

Motivation

• Users were losing subtitle settings when the app was minimized/the screen was turned off, then the app was foregrounded again.

Changes

• Only update selectedTextTrack if there is a value being passed in selectedTextTrackCriteria

Test plan

• On IOS, Play an m3u8 file that includes embedded subtitle tracks such as the sintel with subtitles example
• Choose one of the embedded subtitle tracks
• Minimize the app or turn off the screen
• Foreground the app or turn the screen back on
• The previously selected subtitles should continue to display when the video resumes

[KrzysztofMoch]

LGTM 👍, but should we do same for audioTrack?

[freeboub]

Your patch doesn't look problematic, but I am disturbed as I don't reproduce the issue ... do you have specific props to get the issue ? (maybe you use controls ?)

[Myst1024]

Your patch doesn't look problematic, but I am disturbed as I don't reproduce the issue ... do you have specific props to get the issue ? (maybe you use controls ?)

I have controls={true} and playWhenInactive={true} which I could see contributing to this.
Using version 6.0.0-rc.0