Add null check to walletsync

[xandronus]

When I was resyncing my wallet I got this exception:

Blockcore.AsyncWork.AsyncProvider[0]
      Unhandled exception for async delegate worker WalletSyncManager-blocksQueue.
System.NullReferenceException: Object reference not set to an instance of an object.
   at Blockcore.Features.ColdStaking.ColdStakingManager.ProcessTransaction(Transaction transaction, Nullable`1 blockHeight, Block block, Boolean isPropagated) in C:\source\block-core\blockcore\src\Features\Blockcore.Features.ColdStaking\ColdStakingManager.cs:line 635
   at Blockcore.Features.Wallet.WalletManager.ProcessBlock(Block block, ChainedHeader chainedHeader) in C:\source\block-core\blockcore\src\Features\Blockcore.Features.Wallet\WalletManager.cs:line 1103
   at Blockcore.Features.Wallet.WalletSyncManager.OnProcessBlockAsync(Block block, CancellationToken cancellationToken) in C:\source\block-core\blockcore\src\Features\Blockcore.Features.Wallet\WalletSyncManager.cs:line 240
   at Blockcore.AsyncWork.AsyncQueue`1.ConsumerAsync() in C:\source\block-core\blockcore\src\Blockcore\AsyncWork\AsyncQueue.cs:line 151

Looks like ExtractScriptPubKeyParameters can return null so added null check and wallet was successfully able to sync.

[dangershony]

ah interesting, in what cases you happen to come across that it can be null?

[xandronus]

It was on testnet so might have been malformed transactions or something