patch 8.1.1223: middle mouse click test fails without a clipboard

Problem:    Middle mouse click test fails without a clipboard.
Solution:   Check if the clipboard can be used. (Dominique Pelle, Christian
            Brabandt)  Also use WorkingClipboard() instead of checking for the
            "clipboard" feature.
diff --git a/src/testdir/test_quotestar.vim b/src/testdir/test_quotestar.vim
index c7e38ae..1334201 100644
--- a/src/testdir/test_quotestar.vim
+++ b/src/testdir/test_quotestar.vim
@@ -1,6 +1,7 @@
 " *-register (quotestar) tests
 
-if !has('clipboard')
+source shared.vim
+if !WorkingClipboard()
   finish
 endif