avcodec/ulti: Mark decoder as init-threadsafe

Reviewed-by: Anton Khirnov <anton@khirnov.net>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/ulti.c

@@ -428,4 +428,5 @@ AVCodec ff_ulti_decoder = {
     .close          = ulti_decode_end,
     .decode         = ulti_decode_frame,
     .capabilities   = AV_CODEC_CAP_DR1,
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };