fallback to the BasicConfigurator if no configuration provided

[radist-nt]

According to the logback documentation, logger library initializes itself with BasicConfigurator if no another configuration provided: no configuration file found and no Configurator provided by spi.

logback-config library provides the alternative file format support to logback, so it has to implement the same behavior: fallback to the BasicConfigurator if no hocon configuration provided (i.e., no appenders provided to the root logger after all).