patch 8.1.1874: modeless selection in popup window overlaps scrollbar

Problem:    Modeless selection in popup window overlaps scrollbar.
Solution:   Subtract scrollbar from max_col. (closes #4773)
diff --git a/src/ui.c b/src/ui.c
index 153d020..446cefc 100644
--- a/src/ui.c
+++ b/src/ui.c
@@ -1098,7 +1098,8 @@
 	// Click in a popup window restricts selection to that window,
 	// excluding the border.
 	cb->min_col = wp->w_wincol + wp->w_popup_border[3];
-	cb->max_col = wp->w_wincol + popup_width(wp) - wp->w_popup_border[1];
+	cb->max_col = wp->w_wincol + popup_width(wp)
+				 - wp->w_popup_border[1] - wp->w_has_scrollbar;
 	if (cb->max_col > screen_Columns)
 	    cb->max_col = screen_Columns;
 	cb->min_row = wp->w_winrow + wp->w_popup_border[0];