patch 8.1.0453: MS-Windows: executable() is not reliable

Problem:    MS-Windows: executable() is not reliable.
Solution:   Use $PATHEXT properly. (Yasuhiro Matsumoto, closes #3412)
diff --git a/src/version.c b/src/version.c
index b50ce81..dee74d3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    453,
+/**/
     452,
 /**/
     451,