Fix navigation controller related crashes in iOS 26

[SystemKeeper]

We see crashes inside UIKit like this:

*** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'Cannot display a nested UINavigationController with zero viewControllers: <UINavigationController: 0x10e886000>'

I found one way to reproduce the issue:

• Be in chat A
• Open the menu of the "..." menu, leave it open
• Send a message in chat B
• Tap the push notification that appears
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