patch 8.1.0999: use register one too often and not properly tested

Problem:    Use register one too often and not properly tested.
Solution:   Do not always use register one when specifying a register.
            (closes #4085)  Add more tests.

src/version.c

@@ -779,6 +779,8 @@ static char *(features[]) =
 
 static int included_patches[] =
 {   /* Add new patch number below this line */
+/**/
+    999,
 /**/
     998,
 /**/