fix tx signing with watching only wallets

lib/transaction.py

@@ -677,7 +677,7 @@ class Transaction:
                 'redeemScript':i.get('redeemScript'),
                 'redeemPubkey':i.get('redeemPubkey'),
                 'pubkeys':i.get('pubkeys'),
-                'signatures':i.get('signatures'),
+                'signatures':i.get('signatures',[]),
                 }
             info.append(item)
         return info

lib/wallet.py

@@ -699,6 +699,9 @@ class Wallet:
         
 
     def get_private_key(self, address, password):
+        if self.is_watching_only():
+            return []
+
         # first check the provided password
         seed = self.get_seed(password)