pp_ctl.c: Use macro for when param known non-NULL

There are two versions of this macro; the more general one which checks
for sanity; and another, to be used when its already known that things
are sane.  This commit converts to use the latter, as we do know its
sane here.

Author: khwilliamson

pp_ctl.c

@@ -172,7 +172,7 @@ PP(pp_regcomp)
     }
 
     /* handle the empty pattern */
-    if (!RX_PRELEN(PM_GETRE(pm)) && PL_curpm) {
+    if (!RX_PRELEN(PM_GETRE_raw(pm)) && PL_curpm) {
         if (PL_curpm == PL_reg_curpm) {
             if (PL_curpm_under && PL_curpm_under == PL_reg_curpm) {
                 croak("Infinite recursion via empty pattern");