lnworker: get_channel_by_short_id to use remote scid_alias

This is needed when forwarding payments

electrum/lnworker.py

@@ -1329,6 +1329,8 @@ class LNWallet(LNWorker):
         for chan in self.channels.values():
             if chan.short_channel_id == short_channel_id:
                 return chan
+            if chan.get_remote_scid_alias() == short_channel_id:
+                return chan
 
     def can_pay_invoice(self, invoice: Invoice) -> bool:
         assert invoice.is_lightning()