libfdk-aac: Check if cutoff value is valid

Passing a cutoff value < sample_rate/256 will cause a crash.
Also, values >20000 will have no effect and 20000 will be used anyway.
Signed-off-by: Mohammad Alsaleh <msal@tormail.org>
Signed-off-by: Martin Storsjö <martin@martin.st>

libavcodec/libfdk-aacenc.c

@@ -231,6 +231,11 @@ static av_cold int aac_encode_init(AVCodecContext *avctx)
     }
 
     if (avctx->cutoff > 0) {
+        if (avctx->cutoff < (avctx->sample_rate + 255) >> 8) {
+            av_log(avctx, AV_LOG_ERROR, "cutoff valid range is %d-20000\n",
+                   (avctx->sample_rate + 255) >> 8);
+            goto error;
+        }
         if ((err = aacEncoder_SetParam(s->handle, AACENC_BANDWIDTH,
                                        avctx->cutoff)) != AACENC_OK) {
             av_log(avctx, AV_LOG_ERROR, "Unable to set the encoder bandwith to %d: %s\n",