Multiple threads may try to load the "All" asset library catalogs, so
avoid working on the same catalog service in parallel.
Found when testing #118463 on top of #118382, by creating a sculpt brush
asset while the asset shelf is open. The 3D View header would trigger
reloading of the "All" asset library catalogs to display node assets in
header pulldowns, while the asset shelf triggered a threaded reload of
the asset library.
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