libspeex: allow custom sample rates again.

This was broken by 3b061c5e
Fixes trac issue #1974.
Signed-off-by: Reimar Döffinger <Reimar.Doeffinger@gmx.de>

libavcodec/libspeexdec.c

@@ -51,6 +51,7 @@ static av_cold int libspeex_decode_init(AVCodecContext *avctx)
             av_log(avctx, AV_LOG_WARNING, "Invalid Speex header\n");
     }
     if (header) {
+        avctx->sample_rate = header->rate;
         avctx->channels    = header->nb_channels;
         spx_mode           = header->mode;
         speex_header_free(header);
@@ -73,8 +74,9 @@ static av_cold int libspeex_decode_init(AVCodecContext *avctx)
         av_log(avctx, AV_LOG_ERROR, "Unknown Speex mode %d", spx_mode);
         return AVERROR_INVALIDDATA;
     }
-    avctx->sample_rate = 8000 << spx_mode;
     s->frame_size      =  160 << spx_mode;
+    if (!avctx->sample_rate)
+        avctx->sample_rate = 8000 << spx_mode;
 
     if (avctx->channels < 1 || avctx->channels > 2) {
         /* libspeex can handle mono or stereo if initialized as stereo */