avfilter/avfiltergraph: remove unnecessary channel layout copy

It's not modified, so we can simply use a const pointer to it.
Also check the return value of the other copy in the function while at it.

Reviewed-by: Nicolas George <george@nsup.org>
Signed-off-by: James Almer <jamrial@gmail.com>

libavfilter/avfiltergraph.c

@@ -729,12 +729,12 @@ static int reduce_formats_on_filter(AVFilterContext *filter)
     /* reduce channel layouts */
     for (i = 0; i < filter->nb_inputs; i++) {
         AVFilterLink *inlink = filter->inputs[i];
-        AVChannelLayout fmt = { 0 };
+        const AVChannelLayout *fmt;
 
         if (!inlink->outcfg.channel_layouts ||
             inlink->outcfg.channel_layouts->nb_channel_layouts != 1)
             continue;
-        av_channel_layout_copy(&fmt, &inlink->outcfg.channel_layouts->channel_layouts[0]);
+        fmt = &inlink->outcfg.channel_layouts->channel_layouts[0];
 
         for (j = 0; j < filter->nb_outputs; j++) {
             AVFilterLink *outlink = filter->outputs[j];
@@ -745,24 +745,25 @@ static int reduce_formats_on_filter(AVFilterContext *filter)
                 continue;
 
             if (fmts->all_layouts &&
-                (KNOWN(&fmt) || fmts->all_counts)) {
+                (KNOWN(fmt) || fmts->all_counts)) {
                 /* Turn the infinite list into a singleton */
                 fmts->all_layouts = fmts->all_counts  = 0;
-                if (ff_add_channel_layout(&outlink->incfg.channel_layouts, &fmt) < 0)
+                if (ff_add_channel_layout(&outlink->incfg.channel_layouts, fmt) < 0)
                     ret = 1;
                 break;
             }
 
             for (k = 0; k < outlink->incfg.channel_layouts->nb_channel_layouts; k++) {
-                if (!av_channel_layout_compare(&fmts->channel_layouts[k], &fmt)) {
-                    av_channel_layout_copy(&fmts->channel_layouts[0], &fmt);
+                if (!av_channel_layout_compare(&fmts->channel_layouts[k], fmt)) {
+                    ret = av_channel_layout_copy(&fmts->channel_layouts[0], fmt);
+                    if (ret < 0)
+                        return ret;
                     fmts->nb_channel_layouts = 1;
                     ret = 1;
                     break;
                 }
             }
         }
-        av_channel_layout_uninit(&fmt);
     }
 
     return ret;