CRM-12748, set 0 if do_not_* checkboxes are not checked

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* CRM-12748:
  http://issues.civicrm.org/jira/browse/CRM-12748
Merge pull request #1225 from kurund/CRM-12748

CRM-12748, set 0 if do_not_* checkboxes are not checked
Tested the patch, works as expected now.