avcodec/nellymoserenc: Fix segfault when using unsupported channels/rate

NellyMoserEncodeContext.avctx is only set in init after these checks,
yet it is used by encode_end().
This is a regression since 0a56bfa71f.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/nellymoserenc.c

@@ -138,10 +138,8 @@ static av_cold int encode_end(AVCodecContext *avctx)
 
     ff_mdct_end(&s->mdct_ctx);
 
-    if (s->avctx->trellis) {
-        av_freep(&s->opt);
-        av_freep(&s->path);
-    }
+    av_freep(&s->opt);
+    av_freep(&s->path);
     ff_af_queue_close(&s->afq);
     av_freep(&s->fdsp);