Crash in GPUMessage.cpp when resetting FSocket when RHI is NullRHI.

When tearing down a nanite project with the nullrhi active, there is a crash in the FeedbackManager destructor that causes any exit to be unclean.

The teardown process causes a crash as the destructor relies on GSystem locks that appear to be invalid at this point.

This is an issue as automation that checks for successful completion will halt.

In a nanite-enabled project launched as development no-editor, attempt to cause a clean exit, such as via FPlatformMisc::RequestExitWithStatus(false, 0);

Expected: Clean exit with code 0.
Actual: This should cause an unclean exit as it crashes

ntdll.dll!00007fffdd9ef10d() Unknown
ntdll.dll!00007fffdd9fa6df() Unknown
ntdll.dll!00007fffdd9f9e38() Unknown
> [Inline Frame] UDN18488194.exe!Windows::EnterCriticalSection(Windows::CRITICAL_SECTION *) Line 238 C++
[Inline Frame] UDN18488194.exe!FWindowsCriticalSection::Lock() Line 44 C++
[Inline Frame] UDN18488194.exe!FScopeLock::

{ctor}

(FWindowsCriticalSection *) Line 39 C++
[Inline Frame] UDN18488194.exe!GPUMessage::FSystem::RemoveHandler(TRDGHandle<GPUMessage::FSocket,unsigned int> MessageId) Line 66 C++
UDN18488194.exe!GPUMessage::FSocket::Reset() Line 272 C++
[Inline Frame] UDN18488194.exe!GPUMessage::FSocket::

{dtor}() Line 62 C++
[Inline Frame] UDN18488194.exe!Nanite::FFeedbackManager::{dtor}

() Line 129 C++
UDN18488194.exe!Nanite::FGlobalResources::ReleaseRHI() Line 309 C++
UDN18488194.exe!FRenderResource::ReleaseResource() Line 210 C++
[External Code]