bert for zero shot classification crashes on sentence basis

[ahmedlone127]

Description

This change modifies BertForZeroShotClassification by adding a method for padding with zeros all required arrays inside a batch to ensure all of them have the same length.

How Has This Been Tested?

ran local unit tests that were previously failing

Screenshots (if appropriate):

Types of changes

• [x] Bug fix (non-breaking change which fixes an issue)
• [ ] Code improvements with no or little impact
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• [x] My code follows the code style of this project.
• [ ] My change requires a change to the documentation.
• [ ] I have updated the documentation accordingly.
• [ ] I have read the CONTRIBUTING page.
• [ ] I have added tests to cover my changes.
• [ ] All new and existing tests passed.