libavfilter/af_channelmap: avoid derreferencing possible null

ff_all_channel_layouts() might return null on alloc failure.

Fixes CID1241517
Signed-off-by: Reynaldo H. Verdejo Pinochet <reynaldo@osg.samsung.com>

libavfilter/af_channelmap.c

@@ -287,10 +287,16 @@ static av_cold int channelmap_init(AVFilterContext *ctx)
 static int channelmap_query_formats(AVFilterContext *ctx)
 {
     ChannelMapContext *s = ctx->priv;
+    AVFilterChannelLayouts *layouts;
 
     ff_set_common_formats(ctx, ff_planar_sample_fmts());
     ff_set_common_samplerates(ctx, ff_all_samplerates());
-    ff_channel_layouts_ref(ff_all_channel_layouts(), &ctx->inputs[0]->out_channel_layouts);
+
+    layouts = ff_all_channel_layouts();
+    if (!layouts)
+        return AVERROR(ENOMEM);
+
+    ff_channel_layouts_ref(layouts, &ctx->inputs[0]->out_channel_layouts);
     ff_channel_layouts_ref(s->channel_layouts,       &ctx->outputs[0]->in_channel_layouts);
 
     return 0;