XHR should pass errors to dfd.errBack and not let them bubble up

[dhaber]

In IE (8) if you pass an invalid domain (e.g. ​http://dklfj.sds) as the url to an xhr call (e.g. dojo.xhrPost) IE will throw an exception during the xhr.open() call of dojo.xhr(). This exception will end up bubbling up to the calling code. In other error cases (e.g. when you get a 404 or invalid JSON data) the exception will be properly caught and passed to the deferred's errback. I think this should occur in this case as well.

[bill]

Reassigning to Bryan since he's implementing dojo/request. For you to either fix or mark as "wontfix". I would mark as wontfix because ISTM like a corner case that we shouldn't bother adding any code for.

[Bryan Forbes]

In [28801]:

Wrap xhr.open() call to catch errors. refs #10354 !strict

[Bryan Forbes]

I went ahead and fixed this for two reasons: it was a very simple fix and also every other browser throws the error in the promise chain instead of how IE8 is doing it. Since Dojo's other tools all smooth over browser inconsistencies, I felt this was a great candidate for fixing.