avcodec/utils: Only call codec->close if init has been called

avcodec_open2() also called the AVCodec's close function if an error
happened before init had ever been called if the AVCodec has the
FF_CODEC_CAP_INIT_CLEANUP flag set. This is against the documentation of
said flag: "The codec allows calling the close function for deallocation
even if the init function returned a failure."

E.g. the SVQ3 decoder is not ready to be closed if init has never been
called.

Fixes: NULL dereference
Fixes: 25762/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_SVQ3_fuzzer-5716279070294016

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg

Reviewed-by: Paul B Mahol <onemda@gmail.com>
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavcodec/utils.c

@@ -931,6 +931,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
         || avci->frame_thread_encoder)) {
         ret = avctx->codec->init(avctx);
         if (ret < 0) {
+            codec_init_ok = -1;
             goto free_and_end;
         }
         codec_init_ok = 1;
@@ -1022,8 +1023,8 @@ end:
     return ret;
 free_and_end:
     if (avctx->codec && avctx->codec->close &&
-        (codec_init_ok ||
-         (avctx->codec->caps_internal & FF_CODEC_CAP_INIT_CLEANUP)))
+        (codec_init_ok > 0 || (codec_init_ok < 0 &&
+         avctx->codec->caps_internal & FF_CODEC_CAP_INIT_CLEANUP)))
         avctx->codec->close(avctx);
 
     if (HAVE_THREADS && avci->thread_ctx)