avcodec/tiff: Make decoder init-threadsafe

The only thing that stands in the way of adding the
FF_CODEC_CAP_INIT_THREADSAFE flag to the TIFF decoder is its usage
of ff_codec_open2_recursive(): This function requires its caller to hold
the lock for the mutex that guards initialization of AVCodecContexts
whose codecs have a non-threadsafe init function and only callers whose
codec does not have the FF_CODEC_CAP_INIT_THREADSAFE flag set hold said
lock (the others don't need to care about said lock). But one can set
the flag if one switches to avcodec_open2() at the same time.

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

libavcodec/tiff.c

@@ -2168,7 +2168,7 @@ static av_cold int tiff_init(AVCodecContext *avctx)
     s->avctx_mjpeg->flags2 = avctx->flags2;
     s->avctx_mjpeg->dct_algo = avctx->dct_algo;
     s->avctx_mjpeg->idct_algo = avctx->idct_algo;
-    ret = ff_codec_open2_recursive(s->avctx_mjpeg, codec, NULL);
+    ret = avcodec_open2(s->avctx_mjpeg, codec, NULL);
     if (ret < 0) {
         return ret;
     }
@@ -2219,6 +2219,6 @@ AVCodec ff_tiff_decoder = {
     .close          = tiff_end,
     .decode         = decode_frame,
     .capabilities   = AV_CODEC_CAP_DR1 | AV_CODEC_CAP_FRAME_THREADS,
-    .caps_internal  = FF_CODEC_CAP_INIT_CLEANUP,
+    .caps_internal  = FF_CODEC_CAP_INIT_THREADSAFE | FF_CODEC_CAP_INIT_CLEANUP,
     .priv_class     = &tiff_decoder_class,
 };