patch 8.2.3628: looking terminal colors is a bit slow

Problem:    Looking terminal colors is a bit slow.
Solution:   Cache the terminal colors. (closes #9130, closes #9058)
diff --git a/src/optionstr.c b/src/optionstr.c
index 100b0f4..705e860 100644
--- a/src/optionstr.c
+++ b/src/optionstr.c
@@ -2205,10 +2205,7 @@
     }
     // 'wincolor'
     else if (varp == &curwin->w_p_wcr)
-    {
-	if (curwin->w_buffer->b_term != NULL)
-	    term_update_colors(curwin->w_buffer->b_term);
-    }
+	term_update_wincolor(curwin);
 # if defined(MSWIN)
     // 'termwintype'
     else if (varp == &p_twt)