regcomp.c: Rmv unnecessary code

As spotted by Hugo van der Sanden, a barckwards reference to a capturing
group doesn't need to look forward instead.  If we don't have a
capturing group we already should have, looking forward won't magically
produce it.

Author: khwilliamson

regcomp.c

@@ -11729,16 +11729,8 @@ S_reg(pTHX_ RExC_state_t *pRExC_state, I32 paren, I32 *flagp, U32 depth)
                     num = RExC_npar + num;
                     if (num < 1)  {
 
-                        /* It might be a forward reference; we can't fail until
-                         * we know, by completing the parse to get all the
-                         * groups, and then reparsing */
-                        if (ALL_PARENS_COUNTED)  {
-                            RExC_parse++;
+                        RExC_parse++;
                         vFAIL(non_existent_group_msg);
-                        }
-                        else {
-                            REQUIRE_PARENS_PASS;
-                        }
                     }
                 } else if ( paren == '+' ) {
                     num = RExC_npar + num - 1;

t/re/pat_advanced.t

@@ -2532,6 +2532,13 @@ EOF
                       "", {}, "EXACTFUP node isn't changed into something else");
     }
 
+    {
+        fresh_perl_is('qr/((?-2147483647))/',
+                      "Reference to nonexistent group in regex; marked by <--"
+                    . " HERE in m/((?-2147483647) <-- HERE )/ at - line 1.",
+                      {}, "Large negative relative capture group");
+    }
+
 
     # !!! NOTE that tests that aren't at all likely to crash perl should go
     # a ways above, above these last ones.  There's a comment there that, like