Fix some SOS commands after SharedDomain removal (dotnet/coreclr#21401)

Fix some SOS commands after SharedDomain removal (dotnet/coreclr#21401)

The recent removal of SharedDomain has broken some SOS commands, like
Name2EE or bpmd. There was a code that was enumerating domains and
obtaining some information on them. And the shared domain pointer from
DacpAppDomainStoreData was being included in the list of domains. As it
is NULL now, we have failed to get the information and the domain
iteration loop was exited prematurely.
I have made SOS resilient to the possibility of missing shared domain.
On older runtimes, the shared domain is still being reported.

Commit migrated from https://github.com/dotnet/coreclr/commit/af46c514824aacd4d439eb1891d3d392c6894476