patch 8.1.1509: cmdline_row can become negative, causing a crash

Problem:    Cmdline_row can become negative, causing a crash.
Solution:   Make sure cmdline_row does not become negagive. (closes #4102)
diff --git a/src/version.c b/src/version.c
index 1156fd6..b392cfd 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1509,
+/**/
     1508,
 /**/
     1507,