patch 8.1.0839: when using VTP wrong colors after a color scheme change

Problem:    When using VTP wrong colors after a color scheme change.
Solution:   When VTP is active always clear after a color scheme change.
            (Nobuhiro Takasaki, closes #3872)
diff --git a/src/ex_docmd.c b/src/ex_docmd.c
index dcfdcd4..1646a22 100644
--- a/src/ex_docmd.c
+++ b/src/ex_docmd.c
@@ -7211,6 +7211,15 @@
     }
     else if (load_colors(eap->arg) == FAIL)
 	semsg(_("E185: Cannot find color scheme '%s'"), eap->arg);
+
+#ifdef FEAT_VTP
+    else if (has_vtp_working())
+    {
+	// background color change requires clear + redraw
+	update_screen(CLEAR);
+	redrawcmd();
+    }
+#endif
 }
 
     static void