FlexASIO should allow controlPanel() calls before init()

[dechamps]

In eiz/SynchronousAudioRouter#133 an interesting point was raised, which is that some hosts might want to call controlPanel() before init(). This is somewhat unlikely, and I've never seen an ASIO host application try to do this, but the ASIO SDK doesn't rule this out, so robustness principle would dictate that drivers should be prepared for that to happen.

In the case of FlexASIO, this basically means we should accept controlPanel() calls in the uninitialized state and be prepared to handle such calls without a window handle.

[dechamps]

This is implemented in FlexASIO 1.10.