* Fix suspense crash

* Prevent unmounted suspended vnodes from rendering

Before this when we unmounted a vnode which was in a suspended state
it was possible to cause this to render while being unmounted.
One disturbing thing is that I wanted to check
vnode._component._onResolve
in the options.unmount hook, this however was not possible because
somehow the reference to `_component` isn't being updated on the
vnode that's actually unmounting. For this reason I opted to
use a separate flag.