avserver: do not use a static string as a default for a string option

Fixes an invalid free.

Bug-id: 448

avserver.c

@@ -301,7 +301,7 @@ static int rtp_new_av_stream(HTTPContext *c,
 
 static const char *my_program_name;
 
-static const char *config_filename = "/etc/avserver.conf";
+static const char *config_filename;
 
 static int avserver_debug;
 static int no_launch;
@@ -4633,6 +4633,8 @@ int main(int argc, char **argv)
 {
     struct sigaction sigact = { { 0 } };
 
+    config_filename = av_strdup("/etc/avserver.conf");
+
     parse_loglevel(argc, argv, options);
     av_register_all();
     avformat_network_init();