patch 8.0.0650: for extra help files the filetype is set more than once

Problem:    For extra help files the filetype is set more than once.
Solution:   In *.txt files check that there is no help file modline.
diff --git a/src/version.c b/src/version.c
index 47e1da5..684899e 100644
--- a/src/version.c
+++ b/src/version.c
@@ -765,6 +765,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    650,
+/**/
     649,
 /**/
     648,