patch 8.1.2189: syntax highlighting wrong for tab

Problem:    Syntax highlighting wrong for tab.
Solution:   Don't clear syntax attribute n_extra is non-zero.
diff --git a/src/version.c b/src/version.c
index f11a020..8360988 100644
--- a/src/version.c
+++ b/src/version.c
@@ -742,6 +742,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    2189,
+/**/
     2188,
 /**/
     2187,