R1:083a321dad1b

Fix an issue where newly created Drydock resources could be improperly acquired

Summary:
Ref T9252. This is mostly a fix for an edge case from D14236. Here's the setup:

- There are no resources.
- A request for a new resource arrives.
- We build a new resource.

Now, if we were leasing an existing resource, we'd call `canAcquireLeaseOnResource()` before acquiring a lease on the new resource.

However, for new resources we don't do that: we just acquire a lease immediately. This is wrong, because we…