patch 8.0.0647: syntax highlighting can make cause a freeze

Problem:    Syntax highlighting can make cause a freeze.
Solution:   Apply 'redrawtime' to syntax highlighting, per window.
diff --git a/src/version.c b/src/version.c
index 4683ba4..59f0d09 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    647,
+/**/
     646,
 /**/
     645,