wallet.get_bolt11_invoice: handle request not having LN part

fixes https://github.com/spesmilo/electrum/issues/8402

To reproduce,
- create wallet from a zpub
- LN is disabled there by default
- create a receive request, which won't have a lightning part
- enable config var "bip21_lightning"
- enable LN
- existing request is now ~breaking receive tab

electrum/lnworker.py

@@ -1801,6 +1801,7 @@ class LNWallet(LNWorker):
             fallback_address: Optional[str],
             channels: Optional[Sequence[Channel]] = None,
     ) -> Tuple[LnAddr, str]:
+        assert isinstance(payment_hash, bytes), f"expected bytes, but got {type(payment_hash)}"
 
         pair = self._bolt11_cache.get(payment_hash)
         if pair:
@@ -1856,6 +1857,7 @@ class LNWallet(LNWorker):
             self.wallet.save_db()
 
     def get_preimage(self, payment_hash: bytes) -> Optional[bytes]:
+        assert isinstance(payment_hash, bytes), f"expected bytes, but got {type(payment_hash)}"
         r = self.preimages.get(payment_hash.hex())
         return bytes.fromhex(r) if r else None
 

electrum/wallet.py

@@ -2605,10 +2605,12 @@ class Abstract_Wallet(ABC, Logger, EventListener):
     def get_bolt11_invoice(self, req: Request) -> str:
         if not self.lnworker:
             return ''
+        if (payment_hash := req.payment_hash) is None:  # e.g. req might have been generated before enabling LN
+            return ''
         amount_msat = req.get_amount_msat() or None
         assert (amount_msat is None or amount_msat > 0), amount_msat
         lnaddr, invoice = self.lnworker.get_bolt11_invoice(
-            payment_hash=req.payment_hash,
+            payment_hash=payment_hash,
             amount_msat=amount_msat,
             message=req.message,
             expiry=req.exp,