Check loaded in dac values to avoid SIGSEGV on null pointers

[eterekhin]

Hey, folks!
I've encountered a debugger crash on mac os arm with the attached stack trace.
Looks like we tried to access some field on a null instance.
I went through the code path and added null checks for objects we marshal from the left side.
My change is similar to #104128, but I tried to fix it for the whole Object::ValidateObjectWithPossibleAV method

Code Type: ARM-64 (Native)
OS Version: macOS 14.5 (23F79)

Exception Type: EXC_BAD_ACCESS (SIGSEGV)
Exception Codes: KERN_INVALID_ADDRESS at 0x0000000000000028
Exception Codes: 0x0000000000000001, 0x0000000000000028

Termination Reason: Namespace SIGNAL, Code 11 Segmentation fault: 11
Terminating Process: exc handler [90060]

External Modification Warnings: Process used task_for_pid().

Thread 10 Crashed: 
0   libmscordaccore.dylib                   0x121352b9c MethodTable:: ValidateWithPossibleAV() + 20
1   libmscordaccore.dylib                   0x121381574 DacDbiInterfaceImpl:: FastSanityCheckObject(__DPtr<Object>) + 84
2   libmscordaccore.dylib                   0x121381df0 DacDbiInterfaceImpl:: GetBasicObjectInfo(unsigned long long, CorElementType, VMPTR_Base<AppDomain, __VPtr<AppDomain>>, DebuggerIPCE_ObjectData*) + 104
3   libmscordbi.dylib                       0x120f3a020 CordbReferenceValue:: InitRef(MemoryRange) + 476
4   libmscordbi.dylib                       0x120f3a368 CordbReferenceValue::Dereference(ICorDebugValue**) + 368

[dotnet-policy-service]

Tagging subscribers to this area: @mangod9
See info in area-owners.md if you want to be subscribed.

[huoyaoyuan]

The names of the functions are WithPossibleAV, implies that access violation (SIGSEGV) is a desired behavior.

[eterekhin]

@huoyaoyuan, I've got your point about naming, I understand the naming like we may read at wrong address within the method (the reading happens in DacInstantiateTypeByAddress method), an error will be thrown via EX_THROW macros, mind handling it. But when real AV happens in the program it crashes