patch 8.1.0485: term_start() does not check if directory is accessible

Problem:    term_start() does not check if directory is accessible.
Solution:   Add mch_access() call. (Jason Franklin)
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index b82dae1..235cd31 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -478,6 +478,28 @@
   call delete('Xdir', 'rf')
 endfunc
 
+func Test_terminal_cwd_failure()
+  " Case 1: Provided directory is not actually a directory.  Attempt to make
+  " the file executable as well.
+  call writefile([], 'Xfile')
+  call setfperm('Xfile', 'rwx------')
+  call assert_fails("call term_start(&shell, {'cwd': 'Xfile'})", 'E475:')
+  call delete('Xfile')
+
+  " Case 2: Directory does not exist.
+  call assert_fails("call term_start(&shell, {'cwd': 'Xdir'})", 'E475:')
+
+  " Case 3: Directory exists but is not accessible.
+  call mkdir('Xdir', '', '0600')
+  " return early if the directory permissions could not be set properly
+  if getfperm('Xdir')[2] == 'x'
+    call delete('Xdir', 'rf')
+    return
+  endif
+  call assert_fails("call term_start(&shell, {'cwd': 'Xdir'})", 'E475:')
+  call delete('Xdir', 'rf')
+endfunc
+
 func Test_terminal_servername()
   if !has('clientserver')
     return