patch 9.0.0636: underline color may not work in some terminals

Problem:    Underline color does not work in terminals that don't send a
            termresponse.
Solution:   Do output t_8u if it was set explicitly. (closes #11253)

src/version.c

@@ -699,6 +699,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    636,
 /**/
     635,
 /**/