patch 8.2.0314: short name not set for terminal buffer

Problem:    Short name not set for terminal buffer.
Solution:   Set the short name. (closes #5687)
diff --git a/src/testdir/test_terminal.vim b/src/testdir/test_terminal.vim
index b86614d..20d27bc 100644
--- a/src/testdir/test_terminal.vim
+++ b/src/testdir/test_terminal.vim
@@ -2405,3 +2405,9 @@
     bw!
   endtry
 endfunc
+
+func Test_hidden_terminal()
+  let buf = term_start(&shell, #{hidden: 1})
+  call assert_equal('', bufname('^$'))
+  call StopShellInTerminal(buf)
+endfunc