lavfi/af_channelmap: fix memory leak

Recent commits 6aaac24d and
3835554b made progress towards cleaning
up usage of the formats API, and in particular fixed possible NULL pointer
dereferences.

This commit addresses the issue of possible resource leaks when some intermediate
call fails.

Tested with valgrind --leak-check=full --show-leak-kinds=all, and manual simulation
of malloc/realloc failures.

Fixes: CID 1338330.
Reviewed-by: Paul B Mahol <onemda@gmail.com>
Signed-off-by: Ganesh Ajjanagadde <gajjanagadde@gmail.com>

libavfilter/af_channelmap.c

@@ -292,14 +292,23 @@ static int channelmap_query_formats(AVFilterContext *ctx)
     int ret;
 
     layouts = ff_all_channel_layouts();
+    if (!layouts) {
+        ret = AVERROR(ENOMEM);
+        goto fail;
+    }
     if ((ret = ff_add_channel_layout     (&channel_layouts, s->output_layout                    )) < 0 ||
         (ret = ff_set_common_formats     (ctx             , ff_planar_sample_fmts()             )) < 0 ||
         (ret = ff_set_common_samplerates (ctx             , ff_all_samplerates()                )) < 0 ||
         (ret = ff_channel_layouts_ref    (layouts         , &ctx->inputs[0]->out_channel_layouts)) < 0 ||
         (ret = ff_channel_layouts_ref    (channel_layouts , &ctx->outputs[0]->in_channel_layouts)) < 0)
-        return ret;
+            goto fail;
 
     return 0;
+fail:
+    if (layouts)
+        av_freep(&layouts->channel_layouts);
+    av_freep(&layouts);
+    return ret;
 }
 
 static int channelmap_filter_frame(AVFilterLink *inlink, AVFrame *buf)