patch 8.2.4389: screenpos() does not handle a position in a closed fold

Problem:    screenpos() does not handle a position in a closed fold.
Solution:   Check if the position is inside a closed fold. (closes #9778)

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4389,
 /**/
     4388,
 /**/