Allow empty and zero parts in CallbackData

[uburuntu]

Description

• Allow to use CallbackData with zero parts, next code was raising TypeError:

cb = CallbackData('zero')

• Allow to parts to be empty, next code was raising ValueError:

cb = CallbackData('simple', 'action')
cb.new('')

Type of change

Please delete options that are not relevant.

• New feature (non-breaking change which adds functionality)

How Has This Been Tested?

I added three new tests to cover main usages of CallbackData

Test Configuration:

• Operating System: Windows 10
• Python version: Python 3.8

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• 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