avformat/webmdashenc: Avoid allocation for parsing a number

In order to parse a number from a string, the WebM DASH manifest muxer
would duplicate (via heap-allocation) the part of the string that
contains the number, then read the number via atoi() and then free the
duplicate again. This has been replaced by simply using strtoll() (which
in contrast to atoi() has defined behaviour when the number is not
representable).
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@gmail.com>

libavformat/webmdashenc.c

@@ -425,18 +425,6 @@ static int write_adaptation_set(AVFormatContext *s, int as_index)
     return 0;
 }
 
-static int to_integer(char *p, int len)
-{
-    int ret;
-    char *q = av_malloc(len);
-    if (!q)
-        return AVERROR(ENOMEM);
-    av_strlcpy(q, p, len);
-    ret = atoi(q);
-    av_free(q);
-    return ret;
-}
-
 static int parse_adaptation_sets(AVFormatContext *s)
 {
     WebMDashMuxContext *w = s->priv_data;
@@ -483,7 +471,7 @@ static int parse_adaptation_sets(AVFormatContext *s)
                 return ret;
             q = p;
             while (*q != '\0' && *q != ',' && *q != ' ') q++;
-            as->streams[as->nb_streams - 1] = to_integer(p, q - p + 1);
+            as->streams[as->nb_streams - 1] = strtoll(p, NULL, 10);
             if (as->streams[as->nb_streams - 1] < 0 ||
                 as->streams[as->nb_streams - 1] >= s->nb_streams) {
                 av_log(s, AV_LOG_ERROR, "Invalid value for 'streams' in adapation_sets.\n");