patch 8.1.0055: complete test has wrong order of arguments

Problem:    Complete test has wrong order of arguments. Wrong type for
            sentinel variable.
Solution:   Swap arguments, use VAR_UNKNOWN. (Ozaki Kiichi)

src/mbyte.c

@@ -4799,7 +4799,7 @@ call_imactivatefunc(int active)
 
     argv[0].v_type = VAR_NUMBER;
     argv[0].vval.v_number = active ? 1 : 0;
-    argv[1].v_type = VAR_NUMBER;
+    argv[1].v_type = VAR_UNKNOWN;
     (void)call_func_retnr(p_imaf, 1, argv, FALSE);
 }