patch 8.1.1451: CTRL-L does not clear screen with a popup window

Problem:    CTRL-L does not clear screen with a popup window.
Solution:   Do not change the type to NOT_VALID.  Redraw all windows.
            (closes #4471)
diff --git a/src/version.c b/src/version.c
index 6417e41..6e04c07 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1451,
+/**/
     1450,
 /**/
     1449,