Fixed empty restconf data segv; error restconf quit; etc

lib/src/clixon_json.c

@@ -623,7 +623,7 @@ json_parse(char       *str,
  * @param[in]  str   String containing JSON
  * @param[out] xt    On success a top of XML parse tree is created with name 'top'
  * @retval  0  OK
- * @retval -1  Error with clicon_err called
+ * @retval -1  Error with clicon_err called. Includes parse errors
  *
  * @code
  *  cxobj *cx = NULL;

lib/src/clixon_xml.c

@@ -1355,8 +1355,8 @@ xml_parse_file(int        fd,
  * @param[in]     str   String containing XML definition. 
  * @param[in]     yspec Yang specification, or NULL
  * @param[in,out] xt    Pointer to XML parse tree. If empty will be created.
- * @retval        0  OK
- * @retval       -1  Error with clicon_err called
+ * @retval        0     OK
+ * @retval       -1     Error with clicon_err called. Includes parse error
  *
  * @code
  *  cxobj *xt = NULL;

lib/src/clixon_xml_map.c

@@ -1750,6 +1750,7 @@ xml_merge1(cxobj              *x0,
 /*! Merge XML trees x1 into x0 according to yang spec yspec
  * @note both x0 and x1 need to be top-level trees
  * @see text_modify_top as more generic variant (in datastore text)
+ * @note returns -1 if YANG do not match, you may want to have a softer error
  */
 int
 xml_merge(cxobj     *x0,