AutoDeleter: add operator [] for ArrayDeleter

Change-Id: I015951053050b58e73fd71e4abb104a0755416f7
Reviewed-on: https://review.haiku-os.org/c/haiku/+/2890
Reviewed-by: Adrien Destugues <pulkomandy@gmail.com>
Reviewed-by: Axel Dörfler <axeld@pinc-software.de>

headers/private/shared/AutoDeleter.h

@@ -122,6 +122,11 @@ struct ArrayDeleter : AutoDeleter<C, ArrayDelete<C> >
 {
 	ArrayDeleter() : AutoDeleter<C, ArrayDelete<C> >() {}
 	ArrayDeleter(C *array) : AutoDeleter<C, ArrayDelete<C> >(array) {}
+
+	inline C& operator[](size_t index) const
+	{
+		return this->Get()[index];
+	}
 };