Fixed: instantiating a cib with no owner would generate nil warning

Previously, when a view-based table:

- Had no delegate.
- Used bindings for its data source, thus obviating the need for makeViewWithIdentifier:owner:.

it would eventually call CPCib -instantiateCibWithOwner:topLevelObjects: with a nil owner (the nil table delegate). This method would try to construct a dictionary with the nil owner, which would generate a deprecation warning, and will in the future fail altogether.

In Cocoa, this is exactly what happens, the owner is nil. And the documentation for -instantiateNibWithOwner:topLevelObjects: clearly states that the owner may be nil.

This commit only adds the owner to the name table dictionary if the owner is non-nil. Since objectForKey: with a non-existent key returns nil, this is the same as storing nil for that key.