patch 9.0.1521: failing redo of command with control characters

Problem:    Failing redo of command with control characters.
Solution:   Use AppendToRedobuffLit() for colon commands. (closes #12354)
diff --git a/src/version.c b/src/version.c
index 35ea18a..454e246 100644
--- a/src/version.c
+++ b/src/version.c
@@ -696,6 +696,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1521,
+/**/
     1520,
 /**/
     1519,