Fix for CRM-14375: Membership fee doubled when fixed contribution option set to "no thank you."

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* CRM-14375: Membership fee doubled when fixed contribution option set to "no thank you"
  https://issues.civicrm.org/jira/browse/CRM-14375
Code clean-up. Initialized variables. Removed unused variables.
Resolve PHP notices.
Merge pull request #3037 from GinkgoFJG/CRM-14375

CRM-14375: Membership fee doubled when fixed contribution option set to "no thank you"