patch 8.0.1783: cannot use 256 colors in a MS-Windows console

Problem:    Cannot use 256 colors in a MS-Windows console.
Solution:   Add 256 color support. (Nobuhiro Takasaki, closes #2821)
diff --git a/src/misc1.c b/src/misc1.c
index de79c8e..6c77f4b 100644
--- a/src/misc1.c
+++ b/src/misc1.c
@@ -3723,7 +3723,7 @@
 		    /* No restore color information, refresh the screen. */
 		    if (has_vtp_working() != 0
 # ifdef FEAT_TERMGUICOLORS
-			    && p_tgc
+			    && (p_tgc || (!p_tgc && t_colors >= 256))
 # endif
 			)
 		    {