lnpeer: return fw_info for all parts of a MPP in a trampoline onion

Due to an indendation error, fw_info was returned only for one
HTLC of the MPP. Thus, maybe_fulfill_htlc was called again with
the remaining HTLCs, which could possibly be failed due to MPP
timeout, resulting in fund loss for the forwarder.

electrum/lnpeer.py

@@ -2441,6 +2441,7 @@ class Peer(Logger):
                                 # remove from list of payments, so that another attempt can be initiated
                                 self.lnworker.final_onion_forwardings.remove(payment_key)
                         asyncio.ensure_future(wrapped_callback())
+                    # return fw_info so that maybe_fulfill_htlc will not be called again
                     fw_info = payment_key.hex()
                     return None, fw_info, None
             else: