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/memline.c b/src/memline.c
index e401c73..b6f0300 100644
--- a/src/memline.c
+++ b/src/memline.c
@@ -4860,7 +4860,8 @@
 	     * (happens when all .swp files are in one directory).
 	     */
 	    if (!recoverymode && buf_fname != NULL
-				&& !buf->b_help && !(buf->b_flags & BF_DUMMY))
+				&& !buf->b_help
+				&& !(buf->b_flags & (BF_DUMMY | BF_NO_SEA)))
 	    {
 		int		fd;
 		struct block0	b0;