Fix segmentation fault on Program::__construct() call.

engine/vm.c

@@ -5274,14 +5274,14 @@ PH7_PRIVATE sxi32 PH7_VmByteCodeExec(ph7_vm *pVm) {
 	if(pInstance == 0) {
 		PH7_VmMemoryError(&(*pVm));
 	}
-	/* Enable garbage collector */
-	pInstance->iRef--;
 	/* Check if a constructor is available */
 	pMethod = PH7_ClassExtractMethod(pClass, "__construct", sizeof("__construct") - 1);
 	if(pMethod) {
 		/* Call the class constructor */
 		PH7_VmCallClassMethod(&(*pVm), pInstance, pMethod, 0, 0, 0);
 	}
+	/* Enable garbage collector */
+	pInstance->iRef--;
 	pArgs = ph7_new_array(&(*pVm));
 	sArgv = ph7_new_scalar(&(*pVm));
 	if(!pArgs || !sArgv) {