fix: fixes survey createdBy filtering for null createdBy surveys

[gupta-piyush19]

What does this PR do?

• fixes survey createdBy filtering for null createdBy surveys

Fixes
https://github.com/formbricks/internal/issues/124

How should this be tested?

• Add a new member to the team
• Create a survey using the invited user's account in the invited team.
• Remove the invited user from the team
• Delete the invited user's account
• Now the survey would have null in the createdBy.
• Do the survey filtering, and this survey should be visible under the createdBy:Others filter

Checklist

Required

• Filled out the "How to test" section in this PR
• Read How we Code at Formbricks
• Self-reviewed my own code
• Commented on my code in hard-to-understand bits
• Ran pnpm build
• Checked for warnings, there are none
• Removed all console.logs
• Merged the latest changes from main onto my branch with git pull origin main
• My changes don't cause any responsiveness issues

Appreciated

• If a UI change was made: Added a screen recording or screenshots to this PR
• Updated the Formbricks Docs if changes were necessary

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Name	Status	Preview	Comments	Updated (UTC)
formbricks-cloud	✅ Ready (Inspect)	Visit Preview	💬 Add feedback	May 6, 2024 0:06am

[github-actions]

Thank you for following the naming conventions for pull request titles! 🙏

[mattinannt]

Looks great; thank you :-)