Fix add new action

[PanSpagetka]

When you navigate Control -> Explorer -> Actions -> Configuration -> Add a new action you get following error:

[----] F, [2019-02-27T14:40:55.173928 #11193:2ae5cbf9b8e4] FATAL -- : Error caught: [IndexError] string not matched
/home/rknaur/manageiq-ui-classic/app/controllers/miq_policy_controller/miq_actions.rb:308:in `[]='
/home/rknaur/manageiq-ui-classic/app/controllers/miq_policy_controller/miq_actions.rb:308:in `block in action_build_alert_choices'
/home/rknaur/.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/activerecord-5.0.7.1/lib/active_record/relation/delegation.rb:38:in `each'
/home/rknaur/.rbenv/versions/2.4.3/lib/ruby/gems/2.4.0/gems/activerecord-5.0.7.1/lib/active_record/relation/delegation.rb:38:in `each'
/home/rknaur/manageiq-ui-classic/app/controllers/miq_policy_controller/miq_actions.rb:308:in `reduce'
/home/rknaur/manageiq-ui-classic/app/controllers/miq_policy_controller/miq_actions.rb:308:in `action_build_alert_choices'
/home/rknaur/manageiq-ui-classic/app/controllers/miq_policy_controller/miq_actions.rb:275:in `action_build_edit_screen'
/home/rknaur/manageiq-ui-classic/app/controllers/miq_policy_controller/miq_actions.rb:20:in `action_edit'
/home/rknaur/manageiq-ui-classic/app/controllers/application_controller/explorer.rb:203:in `generic_x_button'
/home/rknaur/manageiq-ui-classic/app/controllers/miq_policy_controller.rb:117:in `x_button'

This PR should fix the error.

Steps for Testing/QA [Optional]

Navigate Control -> Explorer -> Actions -> Configuration -> Add a new action

@mzazrivec please review

[PanSpagetka]

@miq-bot add_label bug
@miq-bot add_label control

[miq-bot]

Checked commits PanSpagetka/manageiq-ui-classic@bf3ceb9~...4828048 with ruby 2.3.3, rubocop 0.52.1, haml-lint 0.20.0, and yamllint 1.10.0
1 file checked, 0 offenses detected
Everything looks fine. 🍰