Fix permission problem

[liaham]

An authorized user for viewing the index page was not able to save
a pivot table query due to some authorization problems.

Tests are also fixed by adding params hash to requests.

[ashrafalzyoud]

ActionView::Template::Error (undefined method `exists?' for File:Class):
13: <%= javascript_include_tag 'd3.min.js', :plugin => 'redmine_pivot_table' %>
14: <%= javascript_include_tag 'c3.min.js', :plugin => 'redmine_pivot_table' %>
15: <%= javascript_include_tag 'c3_renderers.js', :plugin => 'redmine_pivot_table' %>
16: <%= javascript_include_tag @language_js, :plugin => 'redmine_pivot_table', :media => "all" if javascript_exists?(@language_js) %>
17: <% end %>
18:
19: <style>

plugins/redmine_pivot_table/app/helpers/pivottables_helper.rb:114:in `javascript_exists?'
plugins/redmine_pivot_table/app/views/pivottables/index.html.erb:16
plugins/redmine_pivot_table/app/views/pivottables/index.html.erb:9

redmine 5.1.1