patch 8.2.4618: cmdline completion does not recognize single letter commands

Problem:    Command line completion does not recognize single letter commands.
Solution:   Use the condition from find_ex_command().
diff --git a/src/version.c b/src/version.c
index 17d15c0..39eefb5 100644
--- a/src/version.c
+++ b/src/version.c
@@ -751,6 +751,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    4618,
+/**/
     4617,
 /**/
     4616,