chore: Stop passing null buffer when attachment type is invalid on transcript

[KevLehman]

Proposed changes (including videos or screenshots)

Issue(s)

https://rocketchat.atlassian.net/browse/CORE-415

Steps to test or reproduce

Further comments

[dionisio-bot]

Looks like this PR is not ready to merge, because of the following issues:

• This PR is targeting the wrong base branch. It should target 7.5.0, but it targets 7.4.0

Please fix the issues and try again

If you have any trouble, please check the PR guidelines

[changeset-bot]

⚠️ No Changeset found

Latest commit: eff5f9c

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[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 59.44%. Comparing base (2bdab2f) to head (eff5f9c).
Report is 1 commits behind head on develop.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop   #35276   +/-   ##
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  Coverage    59.44%   59.44%           
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  Files         2829     2829           
  Lines        68326    68326           
  Branches     15131    15131           
========================================
  Hits         40614    40614           
  Misses       25054    25054           
  Partials      2658     2658           

Flag	Coverage Δ
unit	75.53% <ø> (ø)

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