Improve handling of faulty binstubs

[Sigurd Meldgaard]

Related to #4225
In case of:

• bad package name
• Failing to parse properties
• ....

We should degrade gracefully.
We could either:

• assert that they are owned by someone else (emit diagnostic, leave binstub, but don't crash)
• assert that they are broken (delete and recreate)

@jonasfj WDYT?