patch 8.1.2031: cursor position wrong when resizing and using conceal

Problem:    Cursor position wrong when resizing and using conceal.
Solution:   Set the flags that the cursor position is valid when setting the
            row and column during redrawing. (closes #4931)

src/screen.c

@@ -5374,6 +5374,7 @@ win_line(
 		wp->w_wcol = col - boguscols;
 	    wp->w_wrow = row;
 	    did_wcol = TRUE;
+	    curwin->w_valid |= VALID_WCOL|VALID_WROW|VALID_VIRTCOL;
 	}
 #endif