XmlGetAttribute returns S_FALSE, not E_NOTFOUND

[wixbot]

Related issue

Issue for the initial "Safe" modifications to evaluate the return values properly.

Originally opened by jchoover

[wixbot]

Release changed from v3.x to v4.x

[barnson]

http://lists.wixtoolset.org/pipermail/wix-devs-wixtoolset.org/2015-October/000132.html provides one reason that S_FALSE isn't entirely evil.

[jchoover]

This still doesn't jive with the behaviors of XmlGetAttribute vs XmlGetAttributeEx.

XmlGetAttributeEx translates S_FALSE to E_NOTFOUND.

XmlGetAttribute does not, and returns S_FALSE.

Since XmlGetAttributeNumber calls XmlGetAttributeNumberBase which calls XmlGetAttribute, then there is probably a bug here
https://github.com/wixtoolset/wix4/blob/develop/src/burn/engine/container.cpp#L62

[rseanhall]

I added the ExitOnOptionalXmlQueryFailure and ExitOnRequiredXmlQueryFailure macros in wixtoolset/wix#11 which should abstract away whether S_FALSE or E_NOTFOUND is returned. We can start incrementally using those instead of flipping the switch all at once.

We should fix the example you gave, but I don't think it's a big deal since it's parsing XML that the core toolset created.