verify owner in OEP4 init

[Honglei-Cong]

in OEP4Sample_raiseException.py,
owner-address should be checked to be Base58 address.

[tonyclarking]

The owner address comes from the function "ToScriptHash" method, theoretically, the length should be 20. But no harm to check that the owner address should be legal. I will take that. Many thanks.