patch 8.1.2257: MS-Windows GUI: scroll wheel always uses current window

Problem:    MS-Windows GUI: scroll wheel always uses current window.
Solution:   Add the 'scrollfocus' option for MS-Windows.
diff --git a/src/version.c b/src/version.c
index 182352d..3a8e7ab 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2257,
+/**/
     2256,
 /**/
     2255,