Cosigning requires going through multisig even when all keys are present

[roman-khimov]

$ ./bin/neo-go contract invokefunction -r http://localhost:20332 -w oracle-con.wallet 0xd2a4cff31913016155e38e474a2c06d08be276cf transfer NaLbn4u9rZzk2gifu9hnPtyUbE8mtYZVmT NL8cobmLwM2R99uBPW6uBFvsua9Uzg9YzD 1000000000 "" -- NRBiGqBTmQyPY1RWM669Q9R8yssqS8YRyv 0xfc0b5a05ddde5773671dbabbb0c62461074a3a9e
Enter account NRBiGqBTmQyPY1RWM669Q9R8yssqS8YRyv password > 
failed to push invocation tx: failed to send tx: Invalid Params (-32602) -  - %!s(<nil>)

0xfc0b5a05ddde5773671dbabbb0c62461074a3a9e is a deployed contract that has verify with no parameters, effectively what we need is an empty witness attached to it, but it's not attached and the resulting transaction is broken:

number of signers doesn't match witnesses: 2 vs 1

(notice also that this error could've been returned from RPC server)

1. If we can't properly attach all witnesses, no transaction should be sent (like for proper multisig).
2. If we can do that, then just do that and create valid transaction.