Fix projection crash on empty nested list sub-projection

[glen-84]

Summary

• Queryable projection threw ArgumentException: Property '...' is not defined for type 'List<T>' when a nested list's sub-projection was empty and a scalar sibling followed it. QueryableProjectionListHandler.OnBeforeEnter pushes an instance, but the empty-projection early-return in TryHandleLeave never popped it, so the trailing sibling bound against the leaked list instance.
• The empty-projection branch now pops that instance, keeping the instance stack aligned with the parent scope, mirroring the non-empty path. This is the crash reported in UseProjection drops type-extension resolver fields (v16 regression) #10034.

Test plan

• Added a projection integration test: a non-projectable extension field selected alone inside a nested list, followed by a sibling scalar; it now returns a well-formed result instead of throwing.
• Data.Projections.Tests passes (156 tests).

[Copilot]

Pull request overview

Fixes a crash in queryable projections when a nested list’s sub-projection is empty by ensuring the list handler pops the instance it pushed on enter, keeping the projection context’s instance stack aligned for subsequent sibling selections.

Changes:

• Pop the list instance in QueryableProjectionListHandler.TryHandleLeave when the list sub-projection is empty (prevents sibling scalar binding against the wrong instance).
• Add an integration test covering the “empty nested list sub-projection + trailing sibling scalar” scenario reported in #10034.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
src/HotChocolate/Data/src/Data/Projections/Expressions/Handlers/QueryableProjectionListHandler.cs	Pops the pushed instance on the empty-projection early-return path to prevent instance-stack leakage and downstream binding crashes.
src/HotChocolate/Data/test/Data.Projections.Tests/IntegrationTests.cs	Adds an integration test exercising the empty nested list sub-projection scenario with a trailing sibling scalar field.

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