patch 8.1.0342: crash when a callback deletes a window that is being used

Problem:    Crash when a callback deletes a window that is being used.
Solution:   Do not unload a buffer that is being displayed while redrawing the
            screen. Also avoid invoking callbacks while redrawing.
            (closes #2107)
diff --git a/src/version.c b/src/version.c
index c7787e7..b88258e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -795,6 +795,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    342,
+/**/
     341,
 /**/
     340,