cmdutils: Fix build with lavfi disabled

Signed-off-by: Diego Biurrun <diego@biurrun.de>

cmdutils.c

@@ -1268,6 +1268,7 @@ static void show_help_muxer(const char *name)
         show_help_children(fmt->priv_class, AV_OPT_FLAG_ENCODING_PARAM);
 }
 
+#if CONFIG_AVFILTER
 static void show_help_filter(const char *name)
 {
     const AVFilter *f = avfilter_get_by_name(name);
@@ -1305,6 +1306,7 @@ static void show_help_filter(const char *name)
         show_help_children(f->priv_class, AV_OPT_FLAG_VIDEO_PARAM |
                                           AV_OPT_FLAG_AUDIO_PARAM);
 }
+#endif
 
 int show_help(void *optctx, const char *opt, const char *arg)
 {
@@ -1326,8 +1328,10 @@ int show_help(void *optctx, const char *opt, const char *arg)
         show_help_demuxer(par);
     } else if (!strcmp(topic, "muxer")) {
         show_help_muxer(par);
+#if CONFIG_AVFILTER
     } else if (!strcmp(topic, "filter")) {
         show_help_filter(par);
+#endif
     } else {
         show_help_default(topic, par);
     }