patch 8.1.1520: popup windows are ignored when dealing with mouse position

Problem:    Popup windows are ignored when dealing with mouse position
Solution:   Find the mouse position inside a popup window.  Allow for modeless
            selection.
diff --git a/src/version.c b/src/version.c
index 5c41f4f..8f3d086 100644
--- a/src/version.c
+++ b/src/version.c
@@ -778,6 +778,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1520,
+/**/
     1519,
 /**/
     1518,