Add defensive code

[David Lau]

stacktrace.js/stacktrace.js

Line 106 in c12fccd

 var stackframes = _filtered(ErrorStackParser.parse(error), opts.filter); 

Would it be prudent to add defensive code checking here to make sure ErrorStackParser is not null when this function is being called? In my production, it's possible to invoke fromError when ErrorStackParser is not defined, which causes unhandled JS errors.

[Blake Niemyjski]

Seems like the real issue is that ErrorStackParser is not set, can you submit a test case or snippet that will reproduce this behavior.