patch 8.1.1837: popup test fails if clipboard is supported but not working

Problem:    Popup test fails if clipboard is supported but not working.
Solution:   Add the "clipboard_working" feature. Also use Check commands
            instead of "if" and "throw".  And remove stray ch_logfile().

src/version.c

@@ -769,6 +769,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    1837,
 /**/
     1836,
 /**/