patch 9.0.0812: GUI mouse scrollwheel mappings don't work

Problem:    GUI mouse scrollwheel mappings don't work.
Solution:   Add check for "gui.in_use". (Christopher Plewright, closes #11418)
diff --git a/src/version.c b/src/version.c
index 662835e..f8f0c95 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    812,
+/**/
     811,
 /**/
     810,