patch 9.0.1392: using NULL pointer with nested :open command

Problem:    Using NULL pointer with nested :open command.
Solution:   Check that ccline.cmdbuff is not NULL.
diff --git a/src/version.c b/src/version.c
index 0270abd..9689d8b 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1392,
+/**/
     1391,
 /**/
     1390,