mpeg2: after decoding a picture there's no sliceparsing
mpeg2: after decoding a picture there's no sliceparsing

When a sequence end code comes and the current picture is
decoded parsing slices is not happening anymore

Signed-off-by: Daniel Charles <9f8d44a34cf25995df1daf4e48c6fa87b67d5dc5@intel.com>

YuJiankang/libyami,lizhong1008/libyami,uartie/libyami,YuJiankang/libyami,zhaobob/libyami,clearlylin/libyami,01org/libyami,seanvk/libyami,yizhouwei/libyami,zhaobob/libyami,dspmeng/libyami,01org/libyami,clearlylin/libyami,lizhong1008/libyami,yizhouwei/libyami,seanvk/libyami,chivakker/libyami,zhaobob/libyami,uartie/libyami,seanvk/libyami,yizhouwei/libyami,lizhong1008/libyami,stripes416/libyami,chivakker/libyami,uartie/libyami,dspmeng/libyami,01org/libyami,dspmeng/libyami,stripes416/libyami,YuJiankang/libyami,chivakker/libyami,stripes416/libyami,clearlylin/libyami