opus: always sync i_buffer with i_nb_samples (fixes #10135)
opus: always sync i_buffer with i_nb_samples (fixes #10135)

Specifically, the crash at the end of playback was happening when end trim was
not being subtracted from i_buffer.

xkfz007/vlc,krichter722/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,shyamalschandra/vlc,shyamalschandra/vlc,xkfz007/vlc,xkfz007/vlc,krichter722/vlc,vlc-mirror/vlc,shyamalschandra/vlc,krichter722/vlc,shyamalschandra/vlc,krichter722/vlc,xkfz007/vlc,xkfz007/vlc,vlc-mirror/vlc,krichter722/vlc,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,vlc-mirror/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,xkfz007/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.2,shyamalschandra/vlc,krichter722/vlc,vlc-mirror/vlc,krichter722/vlc,xkfz007/vlc,jomanmuk/vlc-2.2