Don't log unwanted when not initialized

[remicollet]

Messages with severity < treshold should be ignored (always)

For now, when not initialized, appears in stderr:

• a warning message (all log...)
• the unwanted message

See grpc/grpc#37178

[google-cla]

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[remicollet]

Sorry, I don't have any google account, so cannot sign this damned CLA

Feel free to consider this as a bug report, and fix it yourself.