logging before the import starts results in the json-encoded msg being echoed to the screen

[pbiron]

While I was working on Simple namespace-aware parsing, I discovered that any error/warning/etc logging that is done before the actual import starts (e.g., in WXR_Importer::get_preliminary_information()) results in the json-encoded msg being echoed to the screen.

When being run interactively, shouldn't the HTML logger be used for those initial steps and then switch to the ServerSentEvents logger only once the actual import starts?