patch 8.2.1397: Vim9: return type of maparg() not adjusted for fourth arg

Problem:    Vim9: return type of maparg() not adjusted for fourth argument.
Solution:   Check if fourth argument is present. (closes #6645)
diff --git a/src/version.c b/src/version.c
index 8649ca8..b67d3c3 100644
--- a/src/version.c
+++ b/src/version.c
@@ -755,6 +755,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1397,
+/**/
     1396,
 /**/
     1395,