ve.init.mw.ViewPageTarget: Account for serialize error

This is showing a separate need for refactoring. We call
"this.serialize( ..., callback )" but if it failed callback
is never called and an event is emitter for the error.

That makes it rather disconnected from each other.

In this case we're lucky that all calls to serialize are similar
in nature and need the same kind of error callback but other
wise this would be pretty messed up. It obviously needs to be
untangled and get rid of this akward eventemitter dance.

This doesn't fix bug 47581, but it does fix the "Infinite loader
with no error" problem as a result of it by handling the error
in a more intuitive way.

Bug: 47581
Change-Id: Icdf64a792c13a326f494e051be47f2946928d142