Fix NPE when regexp search has no result

[gausie]

Not sure if I need to do anything tests-wise for this (and indeed, how to do that) but I ran into this NPE when adding rhino's compatibility data to core-js (zloirock/core-js#942)

[rbri]

It will be great if you can add a test method that shows the problem to rhino/testsrc/org/mozilla/javascript/tests/es6/NativeRegExpTest.java

[gausie]

Where do I add that test? I'm struggling to navigate the testing setup

[rbri]

I guess you can use the last method in the class I mentioned in my previous comment as a template

[gausie]

@rbri ah, I misread your first message and thought that you were linking me to the source file not the test! Thank you and done - the attached test fails without my change,

[rbri]

Many thanks

[gbrail]

Thanks -- looks mostly great, but I'd like you to look at the handling of the Context object in the text -- see the comment below.

[gbrail]

Thanks for doing this work. I ended up merging and squashing the other version of this PR because both are basically the same. However I just realized that because I "squashed" the PR into one commit, so your name doesn't show up in the commit history directly (although it's in a comment). I'll check more carefully next time -- I want to make sure that we have a diversity of contributors and that people can use work on this project on their "GitHub resume" so let us know if you have other changes to make!