patch 8.0.0522: Win32: when 'clipboard' is "unnamed" yyp does not work

Problem:    MS-Windows: when 'clipboard' is "unnamed" yyp does not work in a
            :global command.
Solution:   When setting the clipboard was postponed, do not clear the
            register.
diff --git a/src/testdir/test_global.vim b/src/testdir/test_global.vim
new file mode 100644
index 0000000..be8aa69
--- /dev/null
+++ b/src/testdir/test_global.vim
@@ -0,0 +1,11 @@
+
+func Test_yank_put_clipboard()
+  new
+  call setline(1, ['a', 'b', 'c'])
+  set clipboard=unnamed
+  g/^/normal yyp
+  call assert_equal(['a', 'a', 'b', 'b', 'c', 'c'], getline(1, 6))
+
+  set clipboard&
+  bwipe!
+endfunc