avcodec/aac_ac3_parser: fix channel information parsing in case decoder is disabled

Fixes #7372

libavcodec/aac_ac3_parser.c

@@ -89,7 +89,7 @@ get_next:
            the frame). */
         if (avctx->codec_id != AV_CODEC_ID_AAC) {
             avctx->sample_rate = s->sample_rate;
-            if (avctx->codec_id != AV_CODEC_ID_EAC3) {
+            if (!CONFIG_EAC3_DECODER || avctx->codec_id != AV_CODEC_ID_EAC3) {
                 avctx->channels = s->channels;
                 avctx->channel_layout = s->channel_layout;
             }
@@ -99,7 +99,7 @@ get_next:
 
         /* Calculate the average bit rate */
         s->frame_number++;
-        if (avctx->codec_id != AV_CODEC_ID_EAC3) {
+        if (!CONFIG_EAC3_DECODER || avctx->codec_id != AV_CODEC_ID_EAC3) {
             avctx->bit_rate +=
                 (s->bit_rate - avctx->bit_rate) / s->frame_number;
         }