transaction.deserialize: more sanity checks

this is mandated by consensus
99813a9745/src/consensus/tx_check.cpp (L13)

electrum/transaction.py

@@ -564,8 +564,12 @@ class Transaction:
             if marker != b'\x01':
                 raise ValueError('invalid txn marker byte: {}'.format(marker))
             n_vin = vds.read_compact_size()
+        if n_vin < 1:
+            raise SerializationError('tx needs to have at least 1 input')
         self._inputs = [parse_input(vds) for i in range(n_vin)]
         n_vout = vds.read_compact_size()
+        if n_vout < 1:
+            raise SerializationError('tx needs to have at least 1 output')
         self._outputs = [parse_output(vds) for i in range(n_vout)]
         if is_segwit:
             for txin in self._inputs: