Guard against non-existing iframes in resize.

[kjarmicki]

Sometimes there are cases when one plugin is removing an iframe and another, called directly after, tries to resize it, which causes errors in Iframe.resize() method (trying to get to style property of element that no longer exists).

This can be guarded against by wrapping styling in a conditional, something like:

if(this.element && this.element.style) {
    this.element.style.width = validSize(this.width);
    this.element.style.height = validSize(this.height);
}

It could also be dealt with in every plugin individually, but I think that would be redundant.

[sveisvei]

Merged, seamed sensible to have a element check.

But should we maybe look into if a removal of the iframe could "stop" the plugin-call-chain?
We could e.g. not allow plugins to remove the iframe directly, but via a remove() on the manager - that correctly "shuts it down".

[kjarmicki]

Yes, that would be a nice enhancement. We still need to check existence of element in resize() tho, because there are cases that this metod could be called outside the plugin.
Take Manager.render() for example, it executes a callback when iframe is rendered. This callback recieves item as an argument and can be called with timeout, keeping item in closure. So there's a possibility that when timeout ends and callback code executes item.iframe.resize(), the actual iframe is gone and that would throw an error.

[sveisvei]

Next release brings a cleanup and rerender setup https://github.com/gardr/host/blob/master/lib/manager.js#L344

[gregersrygg]

@sveisvei Your suggestion about instructing manager to remove an item is interesting. Take a look at the discussion in #25. Maybe we should have a way for plugins to send commands to host/ext?