handle_error_code_from_failed_htlc: fix logic bug
handle_error_code_from_failed_htlc: fix logic bug

the two asserts are supposed to be identical (one was negated)

spesmilo/electrum,spesmilo/electrum,wakiyamap/electrum-mona,wakiyamap/electrum-mona,spesmilo/electrum,wakiyamap/electrum-mona,pooler/electrum-ltc,pooler/electrum-ltc,pooler/electrum-ltc,spesmilo/electrum,pooler/electrum-ltc,wakiyamap/electrum-mona