Prevent compiler warnings and potential OLC setting string truncation.

- Prevented compiler warnings when using
’-Wtautological-pointer-compare’ on development system (Darwin)
- Prevented possible string truncation when adding a newline to an OLC
setting string.

src/act.informative.c

@@ -1698,7 +1698,7 @@ ACMD(do_levels)
   }
   one_argument(argument, arg);
 
-  if (arg != NULL && *arg) {
+  if (*arg) {
     if (isdigit(*arg)) {
       ret = sscanf(arg, "%d-%d", &min_lev, &max_lev);
       if (ret == 0) {