patch 8.2.4106: going over the end of the w_lines array

Problem:    Going over the end of the w_lines array.
Solution:   Break out of the loop when "idx" is too big. (issue #9540)

src/drawscreen.c

@@ -2539,6 +2539,11 @@ win_update(win_T *wp)
 	    eof = TRUE;
 	    break;
 	}
+
+	// Safety check: if any of the wl_size values is wrong we might go over
+	// the end of w_lines[].
+	if (idx >= Rows)
+	    break;
     }
 
     // End of loop over all window lines.

src/version.c

@@ -750,6 +750,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    4106,
 /**/
     4105,
 /**/