avfilter/af_ladspa: set output channel layout for passthrough case

For cases when plugin does not return any samples we just return
input samples. Previously channel layout for outlink was not set.
Set it explicitly instead.
Signed-off-by: Paul B Mahol <onemda@gmail.com>

libavfilter/af_ladspa.c

@@ -612,6 +612,8 @@ static int query_formats(AVFilterContext *ctx)
 
         ff_set_common_channel_layouts(ctx, layouts);
     } else {
+        AVFilterLink *outlink = ctx->outputs[0];
+
         if (s->nb_inputs >= 1) {
             AVFilterLink *inlink = ctx->inputs[0];
             int64_t inlayout = FF_COUNT2LAYOUT(s->nb_inputs);
@@ -619,10 +621,12 @@ static int query_formats(AVFilterContext *ctx)
             layouts = NULL;
             ff_add_channel_layout(&layouts, inlayout);
             ff_channel_layouts_ref(layouts, &inlink->out_channel_layouts);
+
+            if (!s->nb_outputs)
+                ff_channel_layouts_ref(layouts, &outlink->in_channel_layouts);
         }
 
         if (s->nb_outputs >= 1) {
-            AVFilterLink *outlink = ctx->outputs[0];
             int64_t outlayout = FF_COUNT2LAYOUT(s->nb_outputs);
 
             layouts = NULL;