Skip address lookup for PUBLISH error messages (fixes #9)

A publish error is returned to the publisher as a PUBLISH message with
the isError flag set. The publisher is not a MAL provider for the PUBLISH
operation, so the unconditional lookupAddress at the _PUBLISH_STAGE
dispatch always failed for it and logged a spurious warning:
"lookupAddress failed to find local endpoint for ...". Delivery of the
error was unaffected because handlePublish already ignores the address
for error messages and dispatches via the publish listener map.

Only perform the address lookup for non-error PUBLISH messages (the
broker path). The NOTIFY path already avoided the lookup.

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>

Author: CesarCoelho

mal-impl/src/main/java/esa/mo/mal/impl/MALReceiver.java

@@ -189,7 +189,15 @@ public void onMessage(final MALEndpoint callingEndpoint, MALMessage msg) {
                             handlePublishRegister(msg, address);
                             break;
                         case MALPubSubOperation._PUBLISH_STAGE:
-                            address = lookupAddress(callingEndpoint, null);
+                            // Only brokers hold a provider endpoint for the PUBLISH
+                            // operation. A publish error is returned to the publisher
+                            // as a PUBLISH message with the isError flag set; the
+                            // publisher is not a provider, so looking up its (absent)
+                            // address would only log a spurious warning. handlePublish
+                            // does not use the address for error messages anyway.
+                            if (!msg.getHeader().getIsErrorMessage()) {
+                                address = lookupAddress(callingEndpoint, null);
+                            }
                             handlePublish(msg, address);
                             break;
                         case MALPubSubOperation._NOTIFY_STAGE: