Added defensive null checks for db connection

[bogdanfazakas]

Fixes #1155 .

Changes proposed in this PR:

• This PR adds defensive null/undefined checks around oceanNode.getDatabase() and its sub-stores (ddo, ddoState, logs, indexer) to prevent runtime crashes when the DB layer is not initialized / temporarily unavailable.
• Instead of throwing (e.g. Cannot read properties of undefined), affected API handlers now fail gracefully with 503 Service Unavailable, while internal helpers log a warning and return undefined / default values where appropriate.

[bogdanfazakas]

/run-security-scan

[alexcos20]

AI automated code review (Gemini 3).

Overall risk: low

Summary:
This pull request introduces comprehensive null and undefined checks for the database instance and its specific sub-components (like ddo, ddoState, logs, indexer) across various handlers and utility functions. This change significantly improves the robustness of the application by preventing runtime errors that could occur if a database component is unexpectedly unavailable. Error handling for database unavailability is implemented by returning 503 Service Unavailable for API endpoints and logging warnings or returning undefined for internal utility functions.

Comments:
• [INFO][style] The pattern if (!database || !database.ddo) (and similar for other database properties) is repeated across multiple files. While functionally correct, consider if using optional chaining like if (!database?.ddo) could improve conciseness and readability, assuming database could be null/undefined. This would align with modern TypeScript/JavaScript practices.
• [WARNING][other] The use of CORE_LOGGER.logMessage(..., true) here is less explicit about the intended log level compared to CORE_LOGGER.error or CORE_LOGGER.log(LOG_LEVELS_STR.LEVEL_WARN, ...). For consistency and clarity in logging, it would be better to use a specific log level function (e.g., CORE_LOGGER.warn or CORE_LOGGER.info) if available, or CORE_LOGGER.log(LOG_LEVELS_STR.LEVEL_INFO, ...).