[Bug #1177831] Fix generation of code for GROUPREF_EXISTS. Thanks to Andre Malo for the fix.

Lib/sre_compile.py

@@ -167,7 +167,7 @@ def _compile(code, pattern, flags):
             emit(av-1)
         elif op is GROUPREF_EXISTS:
             emit(OPCODES[op])
-            emit((av[0]-1)*2)
+            emit(av[0]-1)
             skipyes = _len(code); emit(0)
             _compile(code, av[1], flags)
             if av[2]: