fix(#1024): Fix validation error on GraphQL request when importing Insomnia collection

[nelup20]

Closes #1024

Description

Changed variables to be an empty string just like query when there's an exception while parsing a GraphQL request.

Before	After
bruno_bugfix_1024_before.mp4	bruno_bugfix_1024_after.mp4

Contribution Checklist:

• The pull request only addresses one issue or adds one feature.
• The pull request does not introduce any breaking changes
• I have added screenshots or gifs to help explain the change if applicable.
• I have read the contribution guidelines.
• Create an issue and link to the pull request.

[helloanoop]

Thanks for taking care of this @nelup20 !

[nelup20]

Thanks for all the merges @helloanoop! I really appreciate your work on Bruno and its welcoming nature (first time contributing to an open source project & I love it 😄)