avcodec/rpza: Mark decoder as init-threadsafe

Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/rpza.c

@@ -296,4 +296,5 @@ const AVCodec ff_rpza_decoder = {
     .close          = rpza_decode_end,
     .decode         = rpza_decode_frame,
     .capabilities   = AV_CODEC_CAP_DR1,
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE,
 };