regtests: rm sleep from "swapserver_forceclose" test

less reliance on timing
(OTOH it hardcodes the output index of the commitment tx... meh)

electrum/commands.py

@@ -1639,7 +1639,8 @@ class Commands(Logger):
     @command('wnpl')
     async def close_channel(self, channel_point, force=False, password=None, wallet: Abstract_Wallet = None):
         """
-        Close a lightning channel
+        Close a lightning channel.
+        Returns txid of closing tx.
 
         arg:str:channel_point:channel point
         arg:bool:force:Force closes (broadcast local commitment transaction)

electrum/lnworker.py

@@ -2288,6 +2288,9 @@ class LNWallet(LNWorker):
     def save_preimage(self, payment_hash: bytes, preimage: bytes, *, write_to_disk: bool = True):
         if sha256(preimage) != payment_hash:
             raise Exception("tried to save incorrect preimage for payment_hash")
+        if self._preimages.get(payment_hash.hex()) is not None:
+            return  # we already have this preimage
+        self.logger.debug(f"saving preimage for {payment_hash.hex()}")
         self._preimages[payment_hash.hex()] = preimage.hex()
         if write_to_disk:
             self.wallet.save_db()