patch 8.2.3638: getcompletion() always passes zero as position

Problem:    getcompletion() always passes zero as position to custom
            completion function.
Solution:   Pass the pattern length. (closes #9173)

src/version.c

@@ -757,6 +757,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3638,
 /**/
     3637,
 /**/