separating "internal error case" and "link failed to shutdown" case

eclair-core/src/main/scala/fr/acinq/eclair/channel/fsm/ErrorHandlers.scala

@@ -135,12 +135,19 @@ trait ErrorHandlers extends CommonHandlers {
         handleMutualClose(bestUnpublishedClosingTx, Left(negotiating))
       // NB: we publish the commitment even if we have nothing at stake (in a dataloss situation our peer will send us an error just for that)
       case hasCommitments: ChannelDataWithCommitments =>
-        if ((e.toAscii == "internal error") || (e.toAscii == "link failed to shutdown")) {
+        if (e.toAscii == "internal error")  {
           // It seems like lnd sends this error whenever something wrong happens on their side, regardless of whether
           // the channel actually needs to be closed. We ignore it to avoid paying the cost of a channel force-close,
           // it's up to them to broadcast their commitment if they wish.
           log.warning("ignoring remote '"+e.toAscii+"', probably coming from lnd")
           stay() sending Warning(d.channelId, "ignoring your '"+e.toAscii+"' to avoid an unnecessary force-close")
+        } else if (e.toAscii == "link failed to shutdown") {
+          // When trying to close a channel with LND older than version 0.18.0,
+          // LND will send an error if there are HTLCs on the channel.
+          // ignoring this error will prevent a force-close.
+          // channel closing is retried upon every reconnect of the channel until there is no more HTLC on the channel
+          log.warning("ignoring remote '"+e.toAscii+"', probably coming from lnd")
+          stay() sending Warning(d.channelId, "ignoring your '"+e.toAscii+"' to avoid an unnecessary force-close")
         } else {
           spendLocalCurrent(hasCommitments)
         }