fix(core-p2p): avoid iterating on non-iterable peerBlocks (#2763)

If peerBlocks is falsy, then "for (const block of peerBlocks) {"
would throw an exception that peerBlocks is not iterable.

packages/core-p2p/src/peer-communicator.ts

@@ -161,6 +161,7 @@ export class PeerCommunicator implements P2P.IPeerCommunicator {
             this.logger.debug(
                 `Peer ${peer.ip} did not return any blocks via height ${fromBlockHeight.toLocaleString()}.`,
             );
+            return [];
         }
 
         // To stay backward compatible, don't assume peers respond with serialized transactions just yet.