lavfi/concat: accept a single segment

Simplify scripting operations, so that n=1 is not to be considered as a
special case.

libavfilter/avf_concat.c

@@ -59,7 +59,7 @@ typedef struct {
 
 static const AVOption concat_options[] = {
     { "n", "specify the number of segments", OFFSET(nb_segments),
-      AV_OPT_TYPE_INT, { .i64 = 2 }, 2, INT_MAX, V|A|F},
+      AV_OPT_TYPE_INT, { .i64 = 2 }, 1, INT_MAX, V|A|F},
     { "v", "specify the number of video streams",
       OFFSET(nb_streams[AVMEDIA_TYPE_VIDEO]),
       AV_OPT_TYPE_INT, { .i64 = 1 }, 0, INT_MAX, V|F },