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/version.c b/src/version.c
index 1bdcaaf..fdbb9a6 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1223,
+/**/
     1222,
 /**/
     1221,