db_mysql: fixes FS#434, Kamailio will eat sometimes 100% CPU due a bug in db_mysql

* Fixes FS#434 reported from Maxim, incorrect mysql API usage for mysql_next_result(..)
* According MySQL doc, return values for mysql_next_result(..) can be the following:
  0 - Successful and there are more results
  -1 - Successful and there are no more results
  >0 - An error occured
* Thus, if there will be an error when reading a next result, the code will be infinitely
  looped in “while” cycle and current process will eat 100% CPU (The mysql_more_results
  will not help here because it just checks a local flag that will be set to TRUE in cases
  when there will be more than one result).
* The solution is to replace " > 0” with " == 0”:
Merge branch 'master' of ssh://git.sip-router.org/sip-router

* 'master' of ssh://git.sip-router.org/sip-router:
  db_mysql: proper handling of mysql_next_result(...) return code
  ims_charging: bugfix: Make ims_charging:ccr_timeouts resettable