Fix data.headers plugin crash

[smfreegard]

Fixes:

[CRIT] [ED90CD6F-BDA8-4E8D-B0D4-370F45CDE561.1] [core] Plugin data.headers failed: TypeError: Cannot read property 'address' of undefined
    at Plugin.exports.from_match (/home/smf/git/Haraka/plugins/data.headers.js:289:54)
    at Object.plugins.run_next_hook (/home/smf/git/Haraka/plugins.js:486:28)
    at callback (/home/smf/git/Haraka/plugins.js:442:32)
    at Plugin.exports.direct_to_mx (/home/smf/git/Haraka/plugins/data.headers.js:259:16)
    at Object.plugins.run_next_hook (/home/smf/git/Haraka/plugins.js:486:28)
    at callback (/home/smf/git/Haraka/plugins.js:442:32)
    at Plugin.exports.user_agent (/home/smf/git/Haraka/plugins/data.headers.js:231:12)
    at Object.plugins.run_next_hook (/home/smf/git/Haraka/plugins.js:486:28)
    at callback (/home/smf/git/Haraka/plugins.js:442:32)
    at Plugin.exports.invalid_return_path (/home/smf/git/Haraka/plugins/data.headers.js:146:12)

Same bug as #1640