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/edit.c b/src/edit.c
index ad25252..4de17aa 100644
--- a/src/edit.c
+++ b/src/edit.c
@@ -5267,7 +5267,7 @@
 	col = mouse_col;
 
 	/* find the window at the pointer coordinates */
-	wp = mouse_find_win(&row, &col);
+	wp = mouse_find_win(&row, &col, FAIL_POPUP);
 	if (wp == NULL)
 	    return;
 	curwin = wp;