Simplify initialization of LoggingHandler.logger.

[benjaminp]

getLogging() was called in the constructor of LoggingHandler. So, there's no reason to have lazy initialization for the logger.

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Fixes #<issue_number_goes_here> ☕️

[minherz]

we should make sure that after close() is called it is no longer possible to use the same logging instance

[minherz]

shouldn't we still reset the logging instance here? since we do not throw exception we need a mechanism to avoid reuse of the potentially closed logging client.

[benjaminp]

The javadoc of Handler.close, which we're overriding here, says:

After close has been called this {@code Handler} should no longer be used.  Method calls may either be silently ignored or may throw runtime exceptions.

It's looks like a closed LoggingImpl will simply drop messages, meeting the behavior specified by the documentation.

[minherz]

The change of this PR is implemented in #812