patch 9.1.0412: typo in regexp_bt.c in DEBUG code

Problem:  typo in regexp_bt.c in DEBUG code, causing
          compile error (@kfleong7, after v9.1.0409)
Solution: Replace bulen by buflen

Signed-off-by: Christian Brabandt <cb@256bit.org>

src/version.c

@@ -704,6 +704,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    412,
 /**/
     411,
 /**/