avcodec/apedec: Allocate decoded_buffer after successful ff_get_buffer()

We need to reset samples in this case to avoid being stuck with incorrect
samples value.

Fixes: OOM
Fixes: Timeout
Fixes: 16627/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5638059583864832
Fixes: 17089/clusterfuzz-testcase-minimized-ffmpeg_AV_CODEC_ID_APE_fuzzer-5672188463546368

Found-by: continuous fuzzing process https://github.com/google/oss-fuzz/tree/master/projects/ffmpeg
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

libavcodec/apedec.c

@@ -1497,6 +1497,14 @@ static int ape_decode_frame(AVCodecContext *avctx, void *data,
     /* reallocate decoded sample buffer if needed */
     decoded_buffer_size = 2LL * FFALIGN(blockstodecode, 8) * sizeof(*s->decoded_buffer);
     av_assert0(decoded_buffer_size <= INT_MAX);
+
+    /* get output buffer */
+    frame->nb_samples = blockstodecode;
+    if ((ret = ff_get_buffer(avctx, frame, 0)) < 0) {
+        s->samples=0;
+        return ret;
+    }
+
     av_fast_malloc(&s->decoded_buffer, &s->decoded_size, decoded_buffer_size);
     if (!s->decoded_buffer)
         return AVERROR(ENOMEM);
@@ -1504,11 +1512,6 @@ static int ape_decode_frame(AVCodecContext *avctx, void *data,
     s->decoded[0] = s->decoded_buffer;
     s->decoded[1] = s->decoded_buffer + FFALIGN(blockstodecode, 8);
 
-    /* get output buffer */
-    frame->nb_samples = blockstodecode;
-    if ((ret = ff_get_buffer(avctx, frame, 0)) < 0)
-        return ret;
-
     s->error=0;
 
     if ((s->channels == 1) || (s->frameflags & APE_FRAMECODE_PSEUDO_STEREO))