patch 9.0.1235: MS-Windows console: not flushing termguicolors

Problem:    MS-Windows console: not flushing termguicolors.
Solution:   Flush termguicolors. (Christopher Plewright, closes #11871)
diff --git a/src/term.c b/src/term.c
index 54da3d7..042b6a6 100644
--- a/src/term.c
+++ b/src/term.c
@@ -3222,7 +3222,7 @@
     vim_snprintf(buf, MAX_COLOR_STR_LEN,
 				  (char *)s, RED(rgb), GREEN(rgb), BLUE(rgb));
 #ifdef FEAT_VTP
-    if (use_wt())
+    if (use_vtp() && (p_tgc || t_colors >= 256))
     {
 	out_flush();
 	buf[1] = '[';