patch 8.1.1998: redraw even when no popup window filter was invoked

Problem:    Redraw even when no popup window filter was invoked.
Solution:   Only redraw when must_redraw was set to a larger value.
diff --git a/src/version.c b/src/version.c
index d933bff..634efd1 100644
--- a/src/version.c
+++ b/src/version.c
@@ -758,6 +758,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1998,
+/**/
     1997,
 /**/
     1996,