fix: Reset forced subs between loads
fix: Reset forced subs between loads

Just as we reset text language and role, we should also reset forced
sub state between load() calls.

Discovered while debugging PR #3459.

Change-Id: I22ef29cb6b14e02ee70503595b1303389260a633

shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player,tvoli/shaka-player,tvoli/shaka-player,shaka-project/shaka-player,shaka-project/shaka-player,tvoli/shaka-player