fix: prevent crash when dragging blocks after rapidly creating projects

[UtkarshAnandd]

Summary

Fixes a crash that could occur when repeatedly using New Project and then Play before dragging a block onto the workspace.

The drag controller could encounter an uninitialised/undefined entry in blockList and attempt to read its connections property. This PR adds a guard in _calculateDragGroup so invalid block entries are safely ignored.

Changes

• Guard _calculateDragGroup against undefined blockList entries.
• Preserve handling for both null and undefined blocks.
• Add a regression test for the undefined-block scenario.

Testing

• Reproduced the issue by clicking Next Project and Play repeatedly, then dragging a block.
• Verified the app no longer crashes.
• Ran the relevant test suite successfully.
• I corrected the typo and added exact reproduction steps to the PR description.

Quick verification:

1. Open Music Blocks.
2. Rapidly create several projects using New Project.
3. Open the latest project.
4. Drag any palette block onto the workspace.

Before this fix, this could crash. With this PR, the block is added normally.

## Category

• Bug fix

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 62.13%. Comparing base (4c41f62) to head (d379194).

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #7985   +/-   ##
=======================================
  Coverage   62.13%   62.13%           
=======================================
  Files         187      187           
  Lines       58275    58275           
=======================================
+ Hits        36209    36211    +2     
+ Misses      22066    22064    -2     

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[walterbender]

Maybe there is a typo in your description? I don't know what the "Next Project" button is, so I don't know how to reproduce this bug or test your solution.

[UtkarshAnandd]

@walterbender Thanks — it was a typo. I meant New Project , not “Next Project.” I’ve updated the PR description with the exact reproduction and verification steps.