patch 8.1.1596: when resizing the screen may draw popup in wrong position

Problem:    When resizing the screen may draw popup in wrong position. (Masato
            Nishihata)
Solution:   Check the popup is not outside of the screen. (fixes #4592)
diff --git a/src/popupwin.c b/src/popupwin.c
index aa8bba0..b9526c7 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -2154,8 +2154,9 @@
 	wp->w_winrow += top_off;
 	wp->w_wincol += left_off;
 
-	// Draw the popup text.
-	win_update(wp);
+	// Draw the popup text, unless it's off screen.
+	if (wp->w_winrow < screen_Rows && wp->w_wincol < screen_Columns)
+	    win_update(wp);
 
 	wp->w_winrow -= top_off;
 	wp->w_wincol -= left_off;