patch 8.1.0505: filter command test may fail if helplang is not set

Problem:    Filter command test may fail if helplang is not set.
Solution:   Set 'helplang' for the test. (James McCoy, closes #3591)
diff --git a/src/testdir/test_filter_cmd.vim b/src/testdir/test_filter_cmd.vim
index 3d802f9..6f40a90 100644
--- a/src/testdir/test_filter_cmd.vim
+++ b/src/testdir/test_filter_cmd.vim
@@ -105,8 +105,11 @@
   unlet test_filter_c
 
   " Test filtering :set command
+  let helplang=&helplang
+  set helplang=en
   let res = join(split(execute("filter /^help/ set"), "\n")[1:], " ")
   call assert_match('^\s*helplang=\w*$', res)
+  let &helplang=helplang
 
   " Test filtering :llist command
   call setloclist(0, [{"filename": "/path/vim.c"}, {"filename": "/path/vim.h"}, {"module": "Main.Test"}])
diff --git a/src/version.c b/src/version.c
index 2c06a0f..5da6027 100644
--- a/src/version.c
+++ b/src/version.c
@@ -793,6 +793,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    505,
+/**/
     504,
 /**/
     503,