No model_path exist check for the XLMRMultiClass class

[sanchit-ahuja]

Describe the bug

There's no model_dir exist check in the XLMRMultiClass class in Dialogy. It creates an instance of the class thereby resulting in the creation of a NoneType object.

To Reproduce
Steps to reproduce the behavior:

1. Instantiate the class with a random model_path

Expected behavior
Creates a NoneType object

Screenshots
If applicable, add screenshots to help explain your problem.

Desktop (please complete the following information):

• OS: [e.g. iOS, Ubuntu, Arch]
• Python version [e.g. 3.8, 3.9]

Additional context
Add any other context about the problem here.