ffserver: deprecate inconsistent parsing behavior of Truncate option

Also make it accept the more consistent behavior (boolean option set to
true when specified).

ffserver.c

@@ -4232,8 +4232,16 @@ static int parse_ffconfig(const char *filename)
         } else if (!av_strcasecmp(cmd, "Truncate")) {
             if (feed) {
                 get_arg(arg, sizeof(arg), &p);
+                /* assume Truncate is true in case no argument is specified */
+                if (!arg[0]) {
+                    feed->truncate = 1;
+                } else {
+                    av_log(NULL, AV_LOG_WARNING,
+                           "Truncate N syntax in configuration file is deprecated, "
+                           "use Truncate alone with no arguments\n");
                     feed->truncate = strtod(arg, NULL);
                 }
+            }
         } else if (!av_strcasecmp(cmd, "FileMaxSize")) {
             if (feed) {
                 char *p1;