patch 8.1.0451: Win32 console: keypad keys don't work

Problem:    Win32 console: keypad keys don't work.
Solution:   Use numbers instead of characters to avoid the value becoming
            negative. (Mike Williams)
diff --git a/src/version.c b/src/version.c
index 88b3a53..a225cb9 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    451,
+/**/
     450,
 /**/
     449,