Fix loading collaborators from storage

[ruggi]

Fix #4521

Problem:

The new collaborators storage logic has two problems:

1. the userbar info uses the current user meta instead of the other data
2. loading users meta from the collabs object may return a null (for collaborators not yet stored), which would break the whole multiplayer

Fix:

1. use the right data
2. make sure to return a default placeholder meta object if collaborators[id] is null, which will be replaced with the right meta once it's available in the storage
3. add a helper to safely get a collaborator meta

[github-actions]

Try me

[relativeci]

Job #9246: Bundle Size — 65.58MiB (~+0.01%).

d2d8401(current) vs 5957b21 master#9237(baseline)

Warning

Bundle contains 67 duplicate packages – View duplicate packages

Bundle metrics   1 change 1 regression

	Current Job #9246	Baseline Job #9237
Initial JS	47.73MiB(~+0.01%)	47.73MiB
Initial CSS	0B	0B
Cache Invalidation	18.32%	18.32%
Chunks	25	25
Assets	29	29
Modules	4420	4420
Duplicate Modules	469	469
Duplicate Code	30.17%	30.17%
Packages	458	458
Duplicate Packages	67	67

Bundle size by type   1 change 1 regression

	Current Job #9246	Baseline Job #9237
JS	65.57MiB (~+0.01%)	65.57MiB
HTML	11.32KiB	11.32KiB

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View job #9246 report View fix/collab-loading branch activity

[github-actions]

Performance test results: