fix: reconstruct omitted payer proof subtrees

Allow payer proof merkle reconstruction to reuse hashes placed at omitted subtree roots instead of descending into already materialized descendants.

Co-Authored-By: OpenAI Codex <noreply@openai.com>

Author: vincenzopalazzo

lightning/src/offers/merkle.rs

@@ -645,9 +645,7 @@ pub(super) fn reconstruct_merkle_root<'a>(
 						Some(tagged_branch_hash_from_engine(branch_tag.clone(), l, r));
 				},
 				(Some(_), None) => {},
-				(None, _) => {
-					return Err(SelectiveDisclosureError::InsufficientMissingHashes);
-				},
+				(None, _) => {},
 			};
 		}
 	}