Fix session reconnect handler

[marcschier]

Proposed changes

Fix regression introduced when adding nullable annotation to reconnect handler

Related Issues

• Fixes Could not reconnect because transport channel is null for reverse connect #3470

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[Copilot]

Pull request overview

This PR fixes a regression that was introduced when nullable annotations were added to the session reconnect handler. The regression incorrectly handled the transportChannel parameter which can legitimately be null during session reconnection scenarios.

Changes:

• Moved the null check for transportChannel from an early position to after the reverse connect logic where it's appropriately handled
• Added proper null safety handling for endpointDescription with a null check before usage
• Added nullable propagation for Server.ApplicationUri property access
• Split the RecreateAsync call logic to properly handle both null and non-null transportChannel cases by calling the appropriate overload