patch 8.2.0359: popup_atcursor() may hang

Problem:    popup_atcursor() may hang. (Yasuhiro Matsumoto)
Solution:   Take the decoration into account. (closes #5728)
diff --git a/src/popupwin.c b/src/popupwin.c
index 45d6488..3c85e3d 100644
--- a/src/popupwin.c
+++ b/src/popupwin.c
@@ -1232,8 +1232,9 @@
 		|| wp->w_popup_pos == POPPOS_BOTLEFT))
 	{
 	    wp->w_wincol = wantcol - 1;
-	    if (wp->w_wincol >= Columns - 1)
-		wp->w_wincol = Columns - 1;
+	    // Need to see at least one character after the decoration.
+	    if (wp->w_wincol > Columns - left_extra - 1)
+		wp->w_wincol = Columns - left_extra - 1;
 	}
     }