Perl 5.38 does not handle empty locale names. Backported upstream fix.

--- a/src/rxvtperl.xs
+++ b/src/rxvtperl.xs
@@ -399,7 +399,7 @@ rxvt_perl_interp::init ()
 {
   if (!perl)
     {
-      rxvt_push_locale (""); // perl init destroys current locale
+      rxvt_push_locale ("C"); // perl init destroys current locale
 
       {
         perl_environ = rxvt_environ;