patch 8.1.0647: MS-Windows: balloon_show() does not handle wide characters

Problem:    MS-Windows: balloon_show() does not handle wide characters.
Solution:   Use CreateWindowExW(). (Yasuhiro Matsumoto, closes #3708)
diff --git a/src/version.c b/src/version.c
index 01593ee..6178a84 100644
--- a/src/version.c
+++ b/src/version.c
@@ -800,6 +800,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    647,
+/**/
     646,
 /**/
     645,