Fix memory leak in an error condition.

[bmah888]

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• Version of iperf3 (or development branch, such as master or
  3.1-STABLE) to which this pull request applies: master

• Issues fixed (if any): memory leak for test->settings #1332

• Brief description of code changes (suitable for use as a commit message):

Fix memory leav in an error condition. We weren't free()-ing test->settings when we bailed out in a certain error state.

[swlars]

Looks good!