Fixes several closely related bugs in Zeroname Plugin, those prevent correct work of other domain resolvers:
1. get(), isDomain(): when an address doesn't look like a valid domain, pass control to the next plugin in a chain.
3. Move the .bit-domain matching logic to a separate method isBitDomain().
2. get(), need(): use isBitDomain(), not isDomain() to check if domain resolving is needed in order to not interfere with other domain resolvers.
4. Also rewrite isAddress() to make it look similar to the new implementation of isDomain().
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