libavformat/segment: change segment_list_size behavior to match hls_list_size behavior.

Make the segment muxer keep segment_list_size segments instead of
segment_list_size + 1 segments. This patch also changes the
documentation for segment_list_size to reduce possible confusion over
how many segments are kept.

this allows the segment list to
be limited to containing only one segment which used to be impossible
because a segment_list_size of 0 kept all the segments and a
segment_list_size of 1 kept 2 segments.

Signed-off-by: Simon Thelen <ffmpeg-dev@c-14.de>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

doc/muxers.texi

@@ -822,7 +822,7 @@ Select the listing format.
 @end table
 
 @item segment_list_size @var{size}
-Update the list file so that it contains at most the last @var{size}
+Update the list file so that it contains at most @var{size}
 segments. If 0 the list file will contain all the segments. Default
 value is 0.
 

libavformat/segment.c

@@ -333,7 +333,7 @@ static int segment_end(AVFormatContext *s, int write_trailer, int is_last)
             seg->segment_list_entries_end = entry;
 
             /* drop first item */
-            if (seg->list_size && seg->segment_count > seg->list_size) {
+            if (seg->list_size && seg->segment_count >= seg->list_size) {
                 entry = seg->segment_list_entries;
                 seg->segment_list_entries = seg->segment_list_entries->next;
                 av_free(entry->filename);