h264-mt: handle NAL_DPAs before calling ff_thread_finish_setup

Since a NAL_DPA can start a new frame it has to be handled before
ff_thread_finish_setup is called.

libavcodec/h264.c

@@ -3816,6 +3816,7 @@ static int decode_nal_units(H264Context *h, const uint8_t *buf, int buf_size)
                 case NAL_PPS:
                     nals_needed = nal_index;
                     break;
+                case NAL_DPA:
                 case NAL_IDR_SLICE:
                 case NAL_SLICE:
                     init_get_bits(&hx->s.gb, ptr, bit_length);