htlcswitch+itest: catch link quit signal when processing hodlQueue

This commit makes sure when processing resolutions, e.g, settling
invoices, when the link is already broken, the process would exit with
an error. This fixes the issue we found in the itest, where an
unexpected empty remote pending commitment was created although the
remote peer is already offline.

contractcourt/channel_arbitrator.go

@@ -2155,6 +2155,20 @@ func (c *ChannelArbitrator) checkRemoteDanglingActions(
 			continue
 		}
 
+		preimageAvailable, err := c.isPreimageAvailable(htlc.RHash)
+		if err != nil {
+			log.Errorf("ChannelArbitrator(%v): failed to query "+
+				"preimage for dangling htlc=%x from remote "+
+				"commitments diff", c.cfg.ChanPoint,
+				htlc.RHash[:])
+
+			continue
+		}
+
+		if preimageAvailable {
+			continue
+		}
+
 		// Dust htlcs can be canceled back even before the commitment
 		// transaction confirms. Dust htlcs are not enforceable onchain.
 		// If another version of the commit tx would confirm we either