Description of problem:
With search query matching 0 hosts, remote execution job schedule page:

Preview keeps screen grayed, without preview window and [close] button at all, not error message shown

And details page (this is only for "Update Package - Katello SSH Default through SSH" template):

In "Preview for target", there is "Warning! error during rendering: undefined method 'operatingsystem' for NilClass::Jail (NilClass)" instead of some simple error message

These two pages does not handle search query returning 0 hosts too well


Version-Release number of selected component (if applicable):
satellite-6.2.6-2.0.el7sat.noarch


How reproducible:
always


Steps to Reproduce:
1. Schedule remote execution job Monitor -> Jobs -> [Run job] with host
   search query "name ~ such_a_host_does_not_exists"
2. Click icon of "eye" to preview matching hosts
3. Also try to schedule with:
     Job category: Katello
     Job template: Update Package...
   and check "Preview for target" section


Actual results:
On schedule page if you click on preview button, it grays the screen and there is no way back.
On details page it shows template rendering warning


Expected results:
Should be possible to close grayed page and instead of template rendering error there should be informative error message like "No host matches the search query"