Refactor and improve Geo::LogCursor and tests

What does this MR do?

It mostly keeps the business logic of Geo::LogCursor untouched. List of the changes:

• Adds one more test case to better coverage
• Refactors code of Geo::LogCursor
• Makes Geo::LogCursor more efficient because it removes redundant Geo::EventLog.any?
• We save 0 to ::Geo::EventLogState on the first iteration now if we have no events yet. It does not change things dramatically but it allowed me to remove two lines of code and it's a little more efficient now.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #11092 (closed)