rtpdec: Don't require frames to start with a Mode A packet

While there is no reason for starting a frame with anything else
than a Mode A packet, some senders seem to consistently use Mode B
packets for everything. This fixes depacketization of such streams.
Signed-off-by: Martin Storsjö <martin@martin.st>

libavformat/rtpdec_h263_rfc2190.c

@@ -132,7 +132,7 @@ static int h263_handle_packet(AVFormatContext *ctx, PayloadContext *data,
     if (!data->buf) {
         /* Check the picture start code, only start buffering a new frame
          * if this is correct */
-        if (!f && len > 4 && AV_RB32(buf) >> 10 == 0x20) {
+        if (len > 4 && AV_RB32(buf) >> 10 == 0x20) {
             int ret = avio_open_dyn_buf(&data->buf);
             if (ret < 0)
                 return ret;