fix(ios): fix external text tracks crashes with m3u8 files

[KrzysztofMoch]

Summary

iOS does not support sideload subtitles for HLS playlist like m3u8. Added a safeguard so that such cases do not crash the application.

Test plan

• example app does not crash when using textTracks with m3u8 as source

[freeboub]

Thank you for the crash fix, but It would be better to make the functionality working :)
I tried on my side without success, can you please do a complementary test ? can you test If this feature working on 5.2 version ?
I know I used it on android, but I am not sure I tested it on ios.
If not working on 5.2 ios, then let's go with it !

[KrzysztofMoch]

Thank you for the crash fix, but It would be better to make the functionality working :)
I tried on my side without success, can you please do a complementary test ? can you test If this feature working on 5.2 version ?
I know I used it on android, but I am not sure I tested it on ios.
If not working on 5.2 ios, then let's go with it !

@freeboub I have checked this and this is not working on 5.2 too (but is not crashing)

[freeboub]

Thank you for the crash fix, but It would be better to make the functionality working :)
I tried on my side without success, can you please do a complementary test ? can you test If this feature working on 5.2 version ?
I know I used it on android, but I am not sure I tested it on ios.
If not working on 5.2 ios, then let's go with it !

@freeboub I have checked this and this is not working on 5.2 too (but is not crashing)

Thank you for the test, so let's go with that

[freeboub]

There again spacing change.
But I accept these one 😆

[freeboub]

@KrzysztofMoch I merged the PR for caching, this Pr now conflct with master... Sorry