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().
diff --git a/src/version.c b/src/version.c
index 852595d..77d9406 100644
--- a/src/version.c
+++ b/src/version.c
@@ -770,6 +770,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1837,
+/**/
     1836,
 /**/
     1835,