avcodec/aac_adtstoasc: fix ASC passthrough on small frames

ASC frames smaller than AAC_ADTS_HEADER_SIZE were being discarded.
Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: James Almer <jamrial@gmail.com>
(cherry picked from commit 0f05f2c7)

libavcodec/aac_adtstoasc_bsf.c

@@ -49,14 +49,14 @@ static int aac_adtstoasc_filter(AVBSFContext *bsfc, AVPacket *out)
     if (ret < 0)
         return ret;
 
+    if (bsfc->par_in->extradata && in->size >= 2 && (AV_RB16(in->data) >> 4) != 0xfff)
+        goto finish;
+
     if (in->size < AAC_ADTS_HEADER_SIZE)
         goto packet_too_small;
 
     init_get_bits(&gb, in->data, AAC_ADTS_HEADER_SIZE * 8);
 
-    if (bsfc->par_in->extradata && show_bits(&gb, 12) != 0xfff)
-        goto finish;
-
     if (avpriv_aac_parse_header(&gb, &hdr) < 0) {
         av_log(bsfc, AV_LOG_ERROR, "Error parsing ADTS frame header!\n");
         ret = AVERROR_INVALIDDATA;