patch 8.1.1392: build failure in tiny version

Problem:    Build failure in tiny version.
Solution:   Define ex_popupclear to ex_ni if not implemented.  Add UNUSED.
diff --git a/src/version.c b/src/version.c
index 5573f44..f8e1d45 100644
--- a/src/version.c
+++ b/src/version.c
@@ -768,6 +768,8 @@
 static int included_patches[] =
 {   /* Add new patch number below this line */
 /**/
+    1392,
+/**/
     1391,
 /**/
     1390,