fix cube validation from updating BasePreAggregation

[ferrants]

Check List

• Tests has been run in packages where changes made if available
• Linter has been run for changed code
• Tests for the changes have been added if not covered yet
• Docs have been added / updated if required

Issue Reference this PR resolves
None

Description of Changes Made (if issue reference is not provided)
Noticed this issue where BasePreAggregation would get updated

[paveltiunov]

@ferrants Hey Matt! Nice catch! I'm curious what was affected by this bug?

[ferrants]

I had been looking into implementing this (#276) last week and stumbled upon it.
Not ready by any means, not even sure if it's going to be necessary, but, there might be some logic in there that could be used for using Rollup Aggregations for querying without time dimension granularity.
master...ferrants:partition-date-range)

[paveltiunov]

@ferrants Gotcha. Thanks!