patch 8.1.1018: window cleared when entering Terminal-Normal twice

Problem:    Window cleared when entering Terminal-Normal twice. (Epheien)
Solution:   Don't cleanup scrollback when there is no postponed scrollback.
            (Christian Brabandt, closes #4126)
diff --git a/src/version.c b/src/version.c
index a49f6fb..18daa06 100644
--- a/src/version.c
+++ b/src/version.c
@@ -780,6 +780,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1018,
+/**/
     1017,
 /**/
     1016,