Fix NPE in XMLConnector.dispose() when init() failed

[Copilot]

When XMLConnector.init() fails (e.g. invalid XML/XSD path), the framework still invokes dispose(), which dereferences the never-assigned xmlInstanceHandler and throws an NPE that masks the original failure cause from test/operation calls.

Changes

• XMLConnector.dispose(): guard against xmlInstanceHandler == null, log at ok level and return instead of throwing.
• Idempotency: null out xmlInstanceHandler in a finally after dispose() so repeated calls are safe (consistent with ConcurrentXMLHandler.dispose() decrementing invokers).
• Logging: guard the config.getXmlFilePath() access so a pre-init dispose can't NPE either.

public void dispose() {
    if (xmlInstanceHandler == null) {
        log.ok("Dispose called but XML handler was not initialized; nothing to release");
        return;
    }
    try {
        xmlInstanceHandler.dispose();
    } finally {
        xmlInstanceHandler = null;
    }
    log.ok("Dispose {0}", config != null ? config.getXmlFilePath() : null);
}

Notes

Aligns with the Connector#dispose() SPI contract (must tolerate failed init and repeated calls). mvn test was not run locally — the sandbox cannot resolve the opendj-parent:5.1.1-SNAPSHOT parent POM from central.sonatype.com.