core/sign_tx: Set decred_script_version to 0 by default for decred coins.

core/src/apps/wallet/sign_tx/decred.py

@@ -61,7 +61,7 @@ class Decred(Bitcoin):
     async def confirm_output(
         self, i: int, txo: TxOutputType, txo_bin: TxOutputBinType
     ) -> None:
-        if txo.decred_script_version is not None and txo.decred_script_version != 0:
+        if txo.decred_script_version != 0:
             raise SigningError(
                 FailureType.ActionCancelled,
                 "Cannot send to output with script version != 0",
@@ -141,10 +141,7 @@ class Decred(Bitcoin):
         await helpers.request_tx_finish(self.tx_req)
 
     def check_prevtx_output(self, txo_bin: TxOutputBinType) -> None:
-        if (
-            txo_bin.decred_script_version is not None
-            and txo_bin.decred_script_version != 0
-        ):
+        if txo_bin.decred_script_version != 0:
             raise SigningError(
                 FailureType.ProcessError,
                 "Cannot use utxo that has script_version != 0",

core/src/apps/wallet/sign_tx/helpers.py

@@ -307,8 +307,12 @@ def sanitize_tx_binoutput(tx: TransactionType, coin: CoinInfo) -> TxOutputBinTyp
 def _sanitize_decred(
     tx: Union[TxInputType, TxOutputType, TxOutputBinType], coin: CoinInfo
 ) -> None:
-    if not coin.decred and tx.decred_script_version is not None:
-        raise SigningError(
-            FailureType.DataError,
-            "Decred details provided but Decred coin not specified.",
-        )
+    if coin.decred:
+        if tx.decred_script_version is None:
+            tx.decred_script_version = 0
+    else:
+        if tx.decred_script_version is not None:
+            raise SigningError(
+                FailureType.DataError,
+                "Decred details provided but Decred coin not specified.",
+            )

core/src/apps/wallet/sign_tx/writers.py

@@ -71,8 +71,7 @@ def write_tx_output(w: Writer, o: TxOutputBinType) -> None:
 
 def write_tx_output_decred(w: Writer, o: TxOutputBinType) -> None:
     write_uint64(w, o.amount)
-    if o.decred_script_version is not None:
-        write_uint16(w, o.decred_script_version)
+    write_uint16(w, o.decred_script_version)
     write_bytes_prefixed(w, o.script_pubkey)