Don't silently kill debug messages

Don't silently kill debug messages

The message handler globally installed by the logger silently drop
messages if the logger is not logging. On top of it, it doesn't log
debug messages by default.

Anything not logged is currently silently discarded. This can come as a
surprise to a developer trying to contribute for the first time and
adding some debug message for some reason.

We're thus trying to strike a middle ground which is that debug messages
get a regular output if the logger isn't interested in them.

Signed-off-by: Kevin Ottens <kevin.ottens@nextcloud.com>