Placeholder View Helper "containerExists" makes no sense

[michalbundyra]

At the moment the public function containerExists does not have any change to work:

because __invoke checks if a name is set it is impossible to call placeholder()
So to check if a placeholder name exists you have to all call
placeholder('foobar')->containerExists('foobar')

but then the container is created in __invoke and containerExists returns in every case true.

And because placeholder('dummy') returns a container containerExists is never reachable and usable.

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Originally posted by @bernhard-efler at zendframework/zend-view#16