patch 8.1.2338: using Visual mark sith :s gives E20 if not set

Problem:    Using Visual mark sith :s gives E20 if not set.
Solution:   Ignore errors when handling 'incsearch'. (closes #3837)
diff --git a/src/version.c b/src/version.c
index 996c3c5..67ea6af 100644
--- a/src/version.c
+++ b/src/version.c
@@ -738,6 +738,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2338,
+/**/
     2337,
 /**/
     2336,