libtracker-miner: Be smarter at not triggering TrackerDecorator activity
libtracker-miner: Be smarter at not triggering TrackerDecorator activity

There's times where tracker-extract GraphUpdated handler will fire due
to its own inserts. Doing so is harmless, but triggers each time a
query for the count of unhandled elements that effectively goes nowhere
as it's already active.

So handle_updates() is now smarter at not triggering activity unless
a resource of the inspected classes is added, and graph_updated_cb()
won't trigger anymore the count query everytime.

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