[release/9.0-staging] Bugfix InvalidOperationException/IndexOutOfRangeException in HttpListener.EndGetContext

[github-actions]

Backport of #107804 to release/9.0-staging
Fixes #107025

/cc @rokonec @pjannesen

Customer Impact

Reported by customer in #107025. Affects their admin access to services - causes reliability problem.

Regression

From .NET Framework

Testing

Note: The problem is intermittent and hard to reproduce.
Manual testing has been performed - customer validated with private patch prior to submitting .NET 10 PR - see #107025 (comment)

Risk

Low - these simple changes do not add or modify complex logic

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[karelz]

Looks like we could have used DisconnectResults directly, there was no need to put it into a variable - that is a cosmetic change.
The real meaningful change is protecting the dictionary from unlocked access - which happened in 2 places.

[rokonec]

I think it would would work even without using local variable disconnectResults however using it will not harm anything and could have slightly better runtime performance by not calling DisconnectResults getter multiple time.

Changes looks safe and correct to me.

[karelz]

It is worth fixing in servicing to unblock customers. Marking as such.

[pjannesen]

I think it would would work even without using local variable disconnectResults however using it will not harm anything and could have slightly better runtime performance by not calling DisconnectResults getter multiple time.

The reason behind the local variable is that the getter results in a Volatile.Read. Which makes it more expensive.

[karelz]

Approved by .NET Shiproom (@SteveMCarroll) over email on 1/8. Marking Servicing-approved.

[rokonec]

/ba-g failing flaky tests most probably unrelated to changes of this PR