patch 9.0.1578: SpellCap highlight not always updated when needed

Problem:    SpellCap highlight not always updated when needed.
Solution:   Handle updating line below closed fold and other situations where
            only part of the window is redrawn. (Luuk van Baal, closes #12428,
            closes #12420)
diff --git a/src/version.c b/src/version.c
index 02be5bf..2e8244d 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1578,
+/**/
     1577,
 /**/
     1576,