avfilter/avf_showvolume: let fade be also exactly 0

Signed-off-by: Paul B Mahol <onemda@gmail.com>

doc/filters.texi

@@ -19936,7 +19936,7 @@ Set channel width, allowed range is [80, 8192]. Default is 400.
 Set channel height, allowed range is [1, 900]. Default is 20.
 @item f
-Set fade, allowed range is [0.001, 1]. Default is 0.95.
+Set fade, allowed range is [0, 1]. Default is 0.95.
 @item c
 Set volume color expression.

libavfilter/avf_showvolume.c

@@ -67,7 +67,7 @@ static const AVOption showvolume_options[] = {
     { "b", "set border width",   OFFSET(b), AV_OPT_TYPE_INT, {.i64=1}, 0, 5, FLAGS },
     { "w", "set channel width",  OFFSET(w), AV_OPT_TYPE_INT, {.i64=400}, 80, 8192, FLAGS },
     { "h", "set channel height", OFFSET(h), AV_OPT_TYPE_INT, {.i64=20}, 1, 900, FLAGS },
-    { "f", "set fade",           OFFSET(f), AV_OPT_TYPE_DOUBLE, {.dbl=0.95}, 0.001, 1, FLAGS },
+    { "f", "set fade",           OFFSET(f), AV_OPT_TYPE_DOUBLE, {.dbl=0.95}, 0, 1, FLAGS },
     { "c", "set volume color expression", OFFSET(color), AV_OPT_TYPE_STRING, {.str="PEAK*255+floor((1-PEAK)*255)*256+0xff000000"}, 0, 0, FLAGS },
     { "t", "display channel names", OFFSET(draw_text), AV_OPT_TYPE_BOOL, {.i64=1}, 0, 1, FLAGS },
     { "v", "display volume value", OFFSET(draw_volume), AV_OPT_TYPE_BOOL, {.i64=1}, 0, 1, FLAGS },