patch 8.1.0609: MS-Windows: unused variable, depending on the Ruby version

Problem:    MS-Windows: unused variable, depending on the Ruby version.
Solution:   Put ruby_sysinit and NtInitialize inside #ifdef and make them
            consistent. (Ken Takata)
diff --git a/src/version.c b/src/version.c
index 8157365..f44167a 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    609,
+/**/
     608,
 /**/
     607,