Fix assertion failure when using -X and lock-file in configuration

When 'lock-file ' was used in configuration at the same time as using -X <lockfile2> in named invocation, there was an invalid logic that would lead to a double isc_mem_strdup() call on the value.

Skip the second allocation if lock-file is being used in configuration, so the is used only single time.

Closes #4386 (closed)

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