core: prevent possible use of uninitialized Component.
core: prevent possible use of uninitialized Component.

There's still a race possible by which multiple Component instance could be instantiated in the scope of a given !ComponentManager, but this was already the case before the change. At least now they always will have their `__init__` method called.

Closes #8658.

git-svn-id: 7bda06b145a4a8e9a7f4be07d7c3eb82923a12d6@10242 af82e41b-90c4-0310-8c96-b1721e28e2e2

netjunki/trac-Pygit2,netjunki/trac-Pygit2,walty8/trac,walty8/trac,jun66j5/trac-ja,walty8/trac,jun66j5/trac-ja,jun66j5/trac-ja,walty8/trac,netjunki/trac-Pygit2,jun66j5/trac-ja