patch 8.2.3916: no error for passing an invalid line number to append()

Problem:    No error for passing an invalid line number to append().
Solution:   In Vim9 script check for a non-negative number. (closes #9417)

src/version.c

@@ -749,6 +749,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    3916,
 /**/
     3915,
 /**/