do not allow channel creation from backup file

electrum/lnworker.py

@@ -779,6 +779,8 @@ class LNWallet(LNWorker):
     def open_channel(self, *, connect_str: str, funding_tx: PartialTransaction,
                      funding_sat: int, push_amt_sat: int, password: str = None,
                      timeout: Optional[int] = 20) -> Tuple[Channel, PartialTransaction]:
+        if self.wallet.is_lightning_backup():
+            raise BaseException(_('Cannot create channel: this is a backup file'))
         if funding_sat > LN_MAX_FUNDING_SAT:
             raise Exception(_("Requested channel capacity is over protocol allowed maximum."))
         coro = self._open_channel_coroutine(connect_str=connect_str, funding_tx=funding_tx, funding_sat=funding_sat,