send: avoid build transaction with zero amount

Signed-off-by: Luca Vaccaro <[email protected]>

Author: lvaccaro

gaios/Sendflow/Controllers/SendAmountViewController.swift

@@ -338,7 +338,7 @@ class SendAmountViewController: KeyboardViewController {
             infoView.isHidden = false
         } else {
             btnNextEnabled = false
-            if viewModel.createTx.satoshi != nil || viewModel.createTx.sendAll || viewModel.createTx.txType == .sweep || viewModel.createTx.txType == .redepositExpiredUtxos {
+            if viewModel.createTx.satoshi ?? 0 > 0 || viewModel.createTx.sendAll || viewModel.createTx.txType == .sweep || viewModel.createTx.txType == .redepositExpiredUtxos {
                 btnNextEnabled = true
             }
             lblError.text = ""

gaios/Sendflow/ViewModels/SendAmountViewModel.swift

@@ -36,6 +36,11 @@ class SendAmountViewModel {
     }
 
     var error: String? {
+        if transaction?.txType == .transaction {
+            if !sendAll && (createTx.satoshi ?? 0 == 0) {
+                return nil
+            }
+        }
         if let error = transaction?.error, !error.isEmpty {
             return error
         }
@@ -277,6 +282,8 @@ class SendAmountViewModel {
         case .transaction, .psbt:
             if createTx.sendAll && createTx.satoshi == nil {
                 createTx.satoshi = 0
+            } else if !createTx.sendAll && (createTx.satoshi == nil || createTx.satoshi == 0){
+                return tx
             }
             if let addressee = createTx.addressee {
                 tx.addressees = [addressee]

gaios/Sendflow/ViewModels/SendTxConfirmViewModel.swift

@@ -161,7 +161,7 @@ class SendTxConfirmViewModel {
         }
         bcurUnsignedPsbt = res
     }
-    
+
     func sendPsbt() async throws -> SendTransactionSuccess {
         guard let session = session else {
             throw TransactionError.invalid(localizedDescription: "Invalid session")