locale.c: Remove useless ++ increment

This value is not going to be used again.  I put in the ++ out of habit.

Author: khwilliamson

locale.c

@@ -9962,7 +9962,7 @@ Perl_mem_collxfrm_(pTHX_ const char *input_string,
             }
 
             len = d - sans_highs;
-            *d++ = '\0';
+            *d = '\0';
 
             s = sans_highs;
         }