patch 8.1.1334: when buffer is hidden "F" in 'shortmess' is not used

Problem:    When buffer is hidden "F" in 'shortmess' is not used.
Solution:   Check the "F" flag in 'shortmess' when the buffer is already
            loaded. (Jason Franklin)  Add test_getvalue() to be able to test
            this.
diff --git a/src/testdir/test_options.vim b/src/testdir/test_options.vim
index 6cc0c1a..c5dbb9f 100644
--- a/src/testdir/test_options.vim
+++ b/src/testdir/test_options.vim
@@ -470,13 +470,19 @@
   call assert_match('file2', execute('bn', ''))
   set shortmess+=F
   call assert_true(empty(execute('bn', '')))
+  call assert_false(test_getvalue('need_fileinfo'))
   call assert_true(empty(execute('bn', '')))
+  call assert_false(test_getvalue('need_fileinfo'))
   set hidden
   call assert_true(empty(execute('bn', '')))
+  call assert_false(test_getvalue('need_fileinfo'))
   call assert_true(empty(execute('bn', '')))
+  call assert_false(test_getvalue('need_fileinfo'))
   set nohidden
   call assert_true(empty(execute('bn', '')))
+  call assert_false(test_getvalue('need_fileinfo'))
   call assert_true(empty(execute('bn', '')))
+  call assert_false(test_getvalue('need_fileinfo'))
   set shortmess&
   call assert_match('file1', execute('bn', ''))
   call assert_match('file2', execute('bn', ''))