Y26-109 - [BUG] Re-uploading a multiplexed library manifest that was originally blank causes an error

[BenTopping]

Describe the bug
Re-uploading a multiplexed library manifest that was originally blank causes an error

FreshSerivce/RT Ticket Number
59413

To Reproduce
Steps to reproduce the behaviour:

1. Go to multiplexed library manifest creation and upload a blank one
2. Fill in the multiplexed library manifest with valid data and reupload it
3. See error and cancelled library creation requests

Expected behaviour
The multiplexed library manifest uploads successfully.
Creation requests are not cancelled.

Additional context
This is an edge case. The cancelling requests is to prevent reuploading from partial manifests as downstream tubes would be incorrect. However blank manifests should in theory have no downstream data so should be safe to update.