f: Allow pending finish mempool at HTLC boundary

Let finish return when pending mempool transactions remain but the
safe mining guard refuses to advance into the HTLC fail-back window.
This avoids treating an end-of-input cleanup limitation as a fuzz
crash.

Author: joostjager

fuzz/src/chanmon_consistency.rs

@@ -2585,10 +2585,14 @@ impl<'a, Out: Output + MaybeSend + MaybeSync> Harness<'a, Out> {
 				assert_test_invariants(&self.nodes);
 				return;
 			}
-			assert!(
-				self.mine_blocks(ANTI_REORG_DELAY) > 0,
-				"finish cannot mine pending mempool transactions without crossing an unresolved HTLC timeout deadline"
-			);
+			if self.mine_blocks(ANTI_REORG_DELAY) == 0 {
+				// The input ended with pending mempool transactions but no safe
+				// block left before an HTLC fail-back window. Leave them
+				// unconfirmed rather than forcing finish cleanup to advance
+				// the chain past that boundary.
+				assert_test_invariants(&self.nodes);
+				return;
+			}
 		}
 		assert!(
 			!self.nodes.iter().any(|node| !node.broadcaster.txn_broadcasted.borrow().is_empty())