* YANG when statement in conjunction with grouping/uses/augment

* Several cases were not implemented fully according to RFC 7950
    * Do not extend default values if when statements evaluate to false
    * Do not allow edit-config of nodes if when statements evaluate to false (Sec 8.3.2)
    * If a key leaf is defined in a grouping that is used in a list, the "uses" statement MUST NOT have a "when" statement. (See 7.21.5)
  * See [yang uses's substatement when has no effect #218](https://github.com/clicon/clixon/issues/2$

apps/restconf/restconf_root.c

@@ -380,7 +380,7 @@ api_operations(clicon_handle h,
 	       int           pretty,
 	       restconf_media media_out)
 {
-    int    retval;
+    int    retval = -1;
     cxobj *xerr = NULL;
 
     clicon_debug(1, "%s", __FUNCTION__);