lavf/img2dec: Skip SOS when auto-detecting jpeg.

Improves jpeg auto-detection.

libavformat/img2dec.c

@@ -715,6 +715,7 @@ static int jpeg_probe(AVProbeData *p)
             state = 0xC0;
             break;
         case 0xDA:
+            i += AV_RB16(&b[i + 2]) + 1;
             if (state != 0xC0 && state != 0xDA)
                 return 0;
             state = 0xDA;