fix segfault on unknown long option

src/settings.c

@@ -201,7 +201,7 @@ int settings_load(struct user_settings *s, const char *patharg)
 {
     config_t cfg[1];
     config_setting_t *setting;
-    const char *str;
+    const char *str = NULL;
     
     /* Load default settings */
     ui_defaults(s);

src/toxic.c

@@ -619,6 +619,7 @@ static void parse_args(int argc, char *argv[])
         {"dnslist", required_argument, 0, 'r'},
         {"force-tcp", no_argument, 0, 't'},
         {"proxy", required_argument, 0, 'p'},
+        {NULL, no_argument, NULL, 0},
     };
 
     const char *opts_str = "4bdhotxc:f:n:r:p:";