Fixed: processing spans after SDK is closed (OTel and ASP.NET Core)

[jamescrosswell]

Resolves #3724

Fixes and issue when using ASP.NET Core and OpenTelemetry instrumentation, where the SDK might be closed before the last OpenTelemetry spans get fully processed by the SentrySpanProcessor.

Problem

When the AppBuilderExtensions initialise the SDK a lifetime callback is also registered to close the SDK when the app shuts down:

sentry-dotnet/src/Sentry.AspNetCore/ApplicationBuilderExtensions.cs

Line 45 in e382fb0

lifetime?.ApplicationStopped.Register(SentrySdk.Close);

However this can be called before all telemetry events are received/processed by the SentrySpanProcessor, which was then trying to create new spans for that telemetry using a disabled hub.

Solution

The OnEnd and OnStart events for the SentrySpanProcessor now check to see whether the hub is still active before doing any work.

[bricefriha]

looks good to me