patch 8.1.1813: ATTENTION prompt for a preview popup window

Problem:    ATTENTION prompt for a preview popup window.
Solution:   Close the popup window if aborting the buffer load.  Avoid getting
            the ATTENTION dialog.
diff --git a/src/version.c b/src/version.c
index 71a14ad..7c9ba68 100644
--- a/src/version.c
+++ b/src/version.c
@@ -774,6 +774,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1813,
+/**/
     1812,
 /**/
     1811,