lean-0013: Exported stubs of partial definitions were not marked unsafe

The stubs exported for partial definitions were not marked unsafe. Caught while exporting an exploit during the FRO's bug hunt; not a soundness bug on its own.

Statusfixed
Fixed inv4.33.0
Subsystemelaborator
Guarantee broken—
Mechanism—
Symptom—
Severityhardening
Fools—
Discovery
fro-bug-huntai-assisted
Features
partial
References