patch 8.1.1918: redrawing popups is inefficient

Problem:    Redrawing popups is inefficient.
Solution:   Fix the logic to compute what window lines to redraw.  Make it
            work below the last line.  Remove redrawing all windows.
diff --git a/src/version.c b/src/version.c
index ae4b4e9..c79dfbc 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1918,
+/**/
     1917,
 /**/
     1916,