Fix for #917. Don't clear fragmentedTextBuffer on text track switch.
requested to merge github/fork/MobiTV-AB/fix-for-917-player-freezes-on-fragmented-text-track-change into RC1_v.1.5.2
Created by: TobbeMobiTV
Fix for #917 (closed). Don't clear buffer on switching fragmented text track to avoid that player stalls, and segment fetching does not recover.
It will take some time until new content appear, though. Can be tested with http://vm2.dashif.org/livesim/testpic_2s/multi_subs.mpd