patch 8.1.0912: MS-Windows: warning for signed/unsigned

Problem:    MS-Windows: warning for signed/unsigned.
Solution:   Add type cast. (Nobuhiro Takasaki, closes #3945)
diff --git a/src/version.c b/src/version.c
index 88960ba..343270c 100644
--- a/src/version.c
+++ b/src/version.c
@@ -784,6 +784,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    912,
+/**/
     911,
 /**/
     910,