patch 8.0.1531: cannot use 24 bit colors in MS-Windows console

Problem:    Cannot use 24 bit colors in MS-Windows console.
Solution:   Add support for vcon. (Nobuhiro Takasaki, Ken Takasaki,
            fixes #1270, fixes #2060)
diff --git a/src/screen.c b/src/screen.c
index 8b7a519..9592f55 100644
--- a/src/screen.c
+++ b/src/screen.c
@@ -2177,6 +2177,25 @@
      * End of loop over all window lines.
      */
 
+#ifdef FEAT_VTP
+    /* Rewrite the character at the end of the screen line. */
+    if (use_vtp())
+    {
+	int i;
+
+	for (i = 0; i < Rows; ++i)
+# ifdef FEAT_MBYTE
+	    if (enc_utf8)
+		if ((*mb_off2cells)(LineOffset[i] + Columns - 2,
+					   LineOffset[i] + screen_Columns) > 1)
+		    screen_draw_rectangle(i, Columns - 2, 1, 2, FALSE);
+		else
+		    screen_draw_rectangle(i, Columns - 1, 1, 1, FALSE);
+	    else
+# endif
+		screen_char(LineOffset[i] + Columns - 1, i, Columns - 1);
+    }
+#endif
 
     if (idx > wp->w_lines_valid)
 	wp->w_lines_valid = idx;