Merging of two agglomerates fails in proof reading mode

[valentin-pinkau]

Context

When in proofreading mode merging of two agglomerates fails. More context: https://scm.slack.com/archives/C5AKLAV0B/p1704813184517169

Expected Behavior

The agglomerates should be merged and the annotation should be saved.

Current Behavior

After clicking merge with active segment an error shows up and another toast saying the annotation could not be saved.
There is a log entry in the console: The sagas crashed because of the following error: Error: No mesh data found in state.localSegmentationData.

Steps to Reproduce the bug

1. create volume annotation with a fallback segmentation layer with agglomerate file
2. select proofreading mode
3. Disable automatic loading of meshes
4. merge two agglomerates

Your Environment for b

• Browser name and version: firefox
• Operating System and version: MacOSX

[valentin-pinkau]

fixed in #7534