Add nil checks on the controller module for underlying app

[colin-axner]

Summary

Allow the underlying app to be nil in the ics 27 controller module.

Problem Definition

The underlying app is no longer needed in all cases after adding a msg server to controller and allowing the controller module to claim the channel capability.

Proposal

Add nil checks to all calls on the underlying app within the ics27 controller module. Tests should be added for these checks. To test this case, I believe you'll need to substitute the cbs retrieved from the router with a new IBCMiddleware type which contains nil for the app. It might be best to use a boolean var local to the testing function to see if the nil app should be used for the given test case

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