Improved spu_SortSubpictures.
Improved spu_SortSubpictures.

spu_sys_t::i_channel is not equal to the number of currently used
channels but t is equal to the number of reserved channel since the spu
creation.

jomanmuk/vlc-2.1,shyamalschandra/vlc,shyamalschandra/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,jomanmuk/vlc-2.2,krichter722/vlc,vlc-mirror/vlc-2.1,vlc-mirror/vlc,vlc-mirror/vlc,xkfz007/vlc,jomanmuk/vlc-2.1,krichter722/vlc,shyamalschandra/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,krichter722/vlc,krichter722/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,jomanmuk/vlc-2.1,jomanmuk/vlc-2.1,xkfz007/vlc,xkfz007/vlc,xkfz007/vlc,krichter722/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,krichter722/vlc,vlc-mirror/vlc-2.1,xkfz007/vlc,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.2,vlc-mirror/vlc-2.1,xkfz007/vlc,shyamalschandra/vlc,xkfz007/vlc,shyamalschandra/vlc,shyamalschandra/vlc,jomanmuk/vlc-2.2,vlc-mirror/vlc,jomanmuk/vlc-2.1,krichter722/vlc,vlc-mirror/vlc,jomanmuk/vlc-2.1,vlc-mirror/vlc-2.1,vlc-mirror/vlc-2.1,jomanmuk/vlc-2.1,vlc-mirror/vlc