fix crash on bad xml input

[sstrigler]

fixes #564

[michalwski]

Thanks for the change. Would perfect if you could write a test case showing there was a problem before and now it's fixed.

[sstrigler]

Oh, lol, of course. Not my day. I knew I had forgotten sth. Would have been too easy :p

[sstrigler]

And suddenly a rogue testcase appeared.
[ ] continue
[ ] integration

[michalwski]

Hmm, still the error case is not covered somehow. Take a look here: https://coveralls.io/builds/3999189/source?filename=apps%2Fejabberd%2Fsrc%2Fejabberd_receiver.erl#L336

[sstrigler]

facepalm

[michalwski]

Thanks @sstrigler :)