[mono][hotreload] Ignore if we receive an empty update.

[thaystg]

This PR adds a check to ignore empty hot reload updates in the Mono runtime. This prevents unnecessary processing when ASP.NET Core sends empty updates in WebAssembly debugger scenarios where the debugger itself applies the real updates.
And also avoids assertion for receiving updates from System.Reflection.Metadata.MetadataUpdater.ApplyUpdate and from debugger even if one of them was empty.

[Copilot]

Pull Request Overview

This PR adds a check to ignore empty hot reload updates in the Mono runtime. This prevents unnecessary processing when ASP.NET Core sends empty updates in WebAssembly debugger scenarios where the debugger itself applies the real updates.

Key Changes

• Added early return when both metadata and IL byte counts are zero
• Prevents redundant processing of empty hot reload updates

[thaystg]

/backport to release/10.0

[github-actions]

Started backporting to release/10.0: https://github.com/dotnet/runtime/actions/runs/18202185862

[thaystg]

/backport to release/9.0-staging

[github-actions]

Started backporting to release/9.0-staging: https://github.com/dotnet/runtime/actions/runs/18202189764

[tmat]

Do we need a test?

[steveisok]

Do we need a test?

Can we pull that off in runtime?

[thaystg]

Can we pull that off in runtime

I think it's not possible to add a test here. Not super sure.

[thaystg]

/backport to release/8.0-staging

[github-actions]

Started backporting to release/8.0-staging (link to workflow run)