lnpeer: reject htlcs for alredy paid invoices

Reject new incoming htlcs for requests that have already been paid
before.

Author: f321x

electrum/lnpeer.py

@@ -2580,7 +2580,6 @@ def log_fail_reason(reason: str):
                     fw_payment_key=payment_key)
                 return None, (payment_key, callback)
 
-        # TODO don't accept payments twice for same invoice
         info = self.lnworker.get_payment_info(payment_hash)
         if info is None:
             log_fail_reason(f"no payment_info found for RHASH {htlc.payment_hash.hex()}")
@@ -2616,6 +2615,10 @@ def log_fail_reason(reason: str):
                 log_fail_reason(f"remaining locktime smaller than requested {blocks_to_expiry=} < {info.min_final_cltv_delta=}")
                 raise exc_incorrect_or_unknown_pd
 
+            if info.status == PR_PAID:
+                log_fail_reason(f"invoice has already been paid")
+                raise exc_incorrect_or_unknown_pd
+
             self.lnworker.verified_pending_htlcs[htlc_key] = None
 
         hold_invoice_callback = self.lnworker.hold_invoice_callbacks.get(payment_hash)