Invalid data should cause an error, not a silent placeholder

The behavior is inconsistent between LuaStandalone and LuaSandbox: in
the former, circular data structures and unsupported types cause an
error, while in the latter they are silently replaced with a
"placeholder" object.

The former behavior seems more logical, so let's do that.

Bug: 48393
Change-Id: I99c80549aebbd2ae1b7fbf8ab11f8588b40855fd