avformat/concatdec: set safe mode to enabled instead of auto

This is safer, as a selected demuxer could still mean that it was auto-detected
by a user application
Reviewed-previously-by: Nicolas George <george@nsup.org>
Reviewed-previously-by: Andreas Cadhalpun <andreas.cadhalpun@googlemail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>

doc/demuxers.texi

@@ -104,7 +104,7 @@ All subsequent file-related directives apply to that file.
 
 @item @code{ffconcat version 1.0}
 Identify the script type and version. It also sets the @option{safe} option
-to 1 if it was to its default -1.
+to 1 if it was -1.
 
 To make FFmpeg recognize the format automatically, this directive must
 appears exactly as is (no extra space or byte-order-mark) on the very first
@@ -192,7 +192,9 @@ component.
 
 If set to 0, any file name is accepted.
 
-The default is -1, it is equivalent to 1 if the format was automatically
+The default is 1.
+
+-1 is equivalent to 1 if the format was automatically
 probed and 0 otherwise.
 
 @item auto_convert

libavformat/concatdec.c

@@ -710,7 +710,7 @@ static int concat_seek(AVFormatContext *avf, int stream,
 
 static const AVOption options[] = {
     { "safe", "enable safe mode",
-      OFFSET(safe), AV_OPT_TYPE_BOOL, {.i64 = -1}, -1, 1, DEC },
+      OFFSET(safe), AV_OPT_TYPE_BOOL, {.i64 = 1}, -1, 1, DEC },
     { "auto_convert", "automatically convert bitstream format",
       OFFSET(auto_convert), AV_OPT_TYPE_BOOL, {.i64 = 1}, 0, 1, DEC },
     { "segment_time_metadata", "output file segment start time and duration as packet metadata",