fixup don't UTF8-upgrade caller argument strings

Author: leonerd

pp.c

@@ -7995,9 +7995,11 @@ PP(pp_multiparam)
                 val = svp ? *svp : &PL_sv_undef;
             }
 
-            /* namepv / namelen are always UTF-8 */
             STRLEN namelen;
-            const char *namepv = SvPVutf8(name, namelen);
+            const char *namepv = SvPV(name, namelen);
+            /* namepv / namelen are always UTF-8 */
+            if(!SvUTF8(name))
+                namepv = (const char *)bytes_to_utf8_temp_pv((const U8 *)namepv, &namelen);
 
             U32 namehash;
             PERL_HASH(namehash, namepv, namelen);