Fix exception trying to rpc-load a new chain
Fix exception trying to rpc-load a new chain

Tested with MySQL and PostgreSQL: when the chain is not yet in store,
store.selectall returns None and trying to map that to a tuple throws:
  TypeError: 'NoneType' object is not iterable

So test the result of store.selectall instead - either None or an empty
list will return -1.

Dilmacoin/dilmacoin-abe,Dilmacoin/dilmacoin-abe