Protect against no columns returned in materialized-view (#395)

[the4thamigo-uk]

Summary

If no rows are returned from the query then referencing element 0 fails.

#395

Checklist

Delete items not relevant to your PR:

• Unit and integration tests covering the common scenarios were added
• A human-readable description of the changes was provided to include in CHANGELOG
• For significant changes, documentation in https://github.com/ClickHouse/clickhouse-docs was updated with further explanations or tutorials