Fixed a test failure

src/Compilers/CSharp/Portable/CodeGen/EmitArrayInitializer.cs

@@ -449,7 +449,7 @@ private int TryGetRawDataForArrayInit(BoundArrayInitialization initializer, out
             var initializers = initializer.Initializers;
             if (initializers.Any(init => init.ConstantValue == null))
             {
-                return default;
+                return -1;
             }
 
             var elementCount = initializers.Length;