Add Checks to Dashboard Context

[simianhacker]

This PR fixes #13181 by adding checks to the values before adding queries to the dashboard context filter. The bug was originally introduced in #12624.

This also fixes elastic/beats#4777

[epixa]

@simianhacker Can you add a unit test to this to ensure it doesn't regress in the future? This bug is pretty subtle and has a huge impact

[epixa]

I've confirmed this does fix the beats dashboard issue

[Bargs]

Adding these checks definitely makes dashboard_context more robust and fixes these particular symptoms, but the root issue here is that the query property in the new-style query object is undefined in the first place. It should never be undefined.

This line seems to be the root of all our trouble. It wraps the query even if the query does not exist (as would be the case with old dashboards, Timelion saved visualizations, etc). If we just wrap that line with a conditional, all the errors go away:

if (!_.isUndefined(this.searchSource.getOwn('query'))) {
  this.searchSource.set('query', migrateLegacyQuery(this.searchSource.getOwn('query')));
}

[simianhacker]

Thanks @Bargs, I added that fix as well.

[Bargs]

LGTM

[simianhacker]

Back ported to 6.0 with 9ee0ca8
Back ported to 6.x with 31b3ec2