[Plugin LevelDB] First step of 3414 - Comments and style

[Jim8y]

Description

Credits goes to @cschuchardt88. This is the first task of merging pr-3414 as we discussed. No functional change, just comment and style update. Can be safely merged into master.

Fixes # #3414

Type of change

• Optimization (the change is only an optimization)
• Style (the change is only a code style for better maintenance or standard purpose)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• This change requires a documentation update

Test Configuration:

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes
• Any dependent changes have been merged and published in downstream modules

[roman-khimov]

Missing proper commit description. Still mixing comments and code changes (including new methods) into a single commit.

[roman-khimov]

Does it? Can I go back to "c" in "a b c" after three "Next" calls and !Valid() (ended) iterator?

[Jim8y]

Comemnt is from the @cschuchardt88 pr, i did not really check it, but anyway, if its not yet proper, i will remove it until the last minute.

[roman-khimov]

I'm just suggesting here, I don't know the real behavior, but we want comments to be correct wrt these details.

[roman-khimov]

This was a useful comment after all, the only question is Valid() requirement, please return it (maybe except for Valid() line if we don't know for sure). I'm also not sure Valid() requirement is appropriate for Next() (suppose Prev() at a of a b c and Next() then). Needs to be checked.