patch 8.0.1842: popup menu inside terminal window isn't cleared

Problem:    Popup menu inside terminal window isn't cleared.
Solution:   Use NOT_VALID in pum_undisplay(). (suggested by Christian
            Brabandt, closes #2908)
diff --git a/src/popupmnu.c b/src/popupmnu.c
index 0edfe50..9bebceb 100644
--- a/src/popupmnu.c
+++ b/src/popupmnu.c
@@ -797,7 +797,7 @@
 pum_undisplay(void)
 {
     pum_array = NULL;
-    redraw_all_later(SOME_VALID);
+    redraw_all_later(NOT_VALID);
     redraw_tabline = TRUE;
     status_redraw_all();
 }
diff --git a/src/version.c b/src/version.c
index 67a6acf..af967d1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -762,6 +762,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1842,
+/**/
     1841,
 /**/
     1840,