Pass zero length array as null

Turns out zero length arrays are passed as a pointer to the non-existing element only when the array is passed by reference.

src/coreclr/src/tools/crossgen2/Common/TypeSystem/Interop/IL/Marshaller.cs

@@ -1435,6 +1435,11 @@ protected override void AllocAndTransformManagedToNative(ILCodeStream codeStream
             {
                 ILLocalVariable vPinnedFirstElement = emitter.NewLocal(ManagedElementType.MakeByRefType(), true);
 
+                LoadManagedValue(codeStream);
+                codeStream.Emit(ILOpcode.ldlen);
+                codeStream.Emit(ILOpcode.conv_i4);
+                codeStream.Emit(ILOpcode.brfalse, lNullArray);
+
                 LoadManagedValue(codeStream);
                 codeStream.Emit(ILOpcode.call, emitter.NewToken(getRawSzArrayDataMethod));
                 codeStream.EmitStLoc(vPinnedFirstElement);