update readPicture to make it to read one complete frame at a time for the support of thread-decoding of multi-slice frame.
update readPicture to make it to read one complete frame at a time for the support of thread-decoding of multi-slice frame.

cisco/openh264,cisco/openh264,GuangweiWang/openh264,mstorsjo/openh264,cisco/openh264,mstorsjo/openh264,mstorsjo/openh264,GuangweiWang/openh264,mstorsjo/openh264,GuangweiWang/openh264,GuangweiWang/openh264,cisco/openh264,cisco/openh264,mstorsjo/openh264,GuangweiWang/openh264,GuangweiWang/openh264,mstorsjo/openh264,cisco/openh264,GuangweiWang/openh264,mstorsjo/openh264,cisco/openh264