lnbase: when opening channel, test if we have enough balance first

and make sure we don't try to create the funding txn from local UTXOs

electrum/lnbase.py

@@ -394,6 +394,10 @@ class Peer(PrintError):
 
     @log_exceptions
     async def channel_establishment_flow(self, password, funding_sat, push_msat, temp_channel_id):
+        wallet = self.lnworker.wallet
+        # dry run creating funding tx to see if we even have enough funds
+        funding_tx_test = wallet.mktx([TxOutput(bitcoin.TYPE_ADDRESS, wallet.dummy_address(), funding_sat)],
+                                      password, self.lnworker.config, nonlocal_only=True)
         await self.initialized
         feerate = self.current_feerate_per_kw()
         local_config, per_commitment_secret_seed = self.make_local_config(funding_sat, push_msat, LOCAL)
@@ -454,7 +458,7 @@ class Peer(PrintError):
         redeem_script = funding_output_script(local_config, remote_config)
         funding_address = bitcoin.redeem_script_to_address('p2wsh', redeem_script)
         funding_output = TxOutput(bitcoin.TYPE_ADDRESS, funding_address, funding_sat)
-        funding_tx = self.lnworker.wallet.mktx([funding_output], password, self.lnworker.config)
+        funding_tx = wallet.mktx([funding_output], password, self.lnworker.config, nonlocal_only=True)
         funding_txid = funding_tx.txid()
         funding_index = funding_tx.outputs().index(funding_output)
         # remote commitment transaction