AccountState constructor failure

[Qiao-Jin]

Code below will throw unexpected Exception:

byte[] value = new AccountState()
{
    Votes = new ECPoint[] { ECCurve.Secp256r1.G }
}.ToByteArray();
AccountState state = new AccountState(value);

System.FormatException
StackTrace:
at Neo.IO.Helper.ReadVarInt(BinaryReader reader, UInt64 max)
at Neo.IO.Helper.ReadVarBytes(BinaryReader reader, Int32 max)
at Neo.SmartContract.Helper.DeserializeStackItem(BinaryReader reader, UInt32 maxArraySize, UInt32 maxItemSize)
at Neo.SmartContract.Helper.DeserializeStackItem(Byte[] data, UInt32 maxArraySize, UInt32 maxItemSize)
at Neo.SmartContract.Native.Tokens.Nep5AccountState.FromByteArray(Byte[] data)
at Neo.SmartContract.Native.Tokens.Nep5AccountState..ctor(Byte[] data)
at Neo.SmartContract.Native.Tokens.NeoToken.AccountState..ctor(Byte[] data)
at Neo.UnitTests.SmartContract.Native.Tokens.UT_NeoToken.TestVote()

Test case can be found here:
https://github.com/eryeer/neoUT/blob/1e503440a818c64078f82c3fabcf914994698abe/neo.UnitTests/SmartContract/Native/Tokens/UT_NeoToken.cs#L464-L468

[shargon]

Please review this fix #1006