lnworker: fix get_scid_alias for forwarding

Note: this issue is currently not detected in python unittests,
it shows up only in regtest, and is not currently tested.
One would need to use a proper LNWallet instance in unit tests.

electrum/lnworker.py

@@ -1372,6 +1372,8 @@ class LNWallet(LNWorker):
                 return chan
             if chan.get_remote_scid_alias() == short_channel_id:
                 return chan
+            if chan.get_local_scid_alias() == short_channel_id:
+                return chan
 
     def can_pay_invoice(self, invoice: Invoice) -> bool:
         assert invoice.is_lightning()