mod_groups_internal: Fix traceback when room doesn't exist I'm not sure if it should even be included if it doesn't exist, but I'm not currently sure how this situation occurs, so I'm implementing the lightest possible fix for now.

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summary: Log a message once per minute
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This module sends `-- MARK --` to the log once per minute. This may be
useful to give a sense of how busy the server is or see that logging and
timers are still working.