patch 8.0.1188: autocmd test fails on MS-Windows

Problem:    Autocmd test fails on MS-Windows.
Solution:   Give the buffer a name and find the buffer to be wiped out by
            name.
diff --git a/src/testdir/test_autocmd.vim b/src/testdir/test_autocmd.vim
index eb13563..d0564f3 100644
--- a/src/testdir/test_autocmd.vim
+++ b/src/testdir/test_autocmd.vim
@@ -352,7 +352,9 @@
 " Closing a window might cause an endless loop
 " E814 for older Vims
 func Test_autocmd_bufwipe_in_SessLoadPost()
+  edit Xtest
   tabnew
+  file Xsomething
   set noswapfile
   mksession!
 
@@ -360,7 +362,7 @@
         \ 'let v:swapchoice="e"',
         \ 'augroup test_autocmd_sessionload',
         \ 'autocmd!',
-        \ 'autocmd SessionLoadPost * 4bw!',
+        \ 'autocmd SessionLoadPost * exe bufnr("Xsomething") . "bw!"',
         \ 'augroup END',
 	\ '',
 	\ 'func WriteErrors()',