Merge branch 'fix_trigger_search' into 'master'

Only trigger search if search string is present

This is a follow up for !296 to prevent the search function from being executed while the query is nil.

Problem was this:
When the search is called, the search controller gets 2 requests.
```
{"action"=>"show", "controller"=>"search"}
```
and
```
{"utf8"=>"✓",
 "search"=>"proj",
 "project_id"=>"",
 "group_id"=>"",
 "snippets"=>"",
 "scope"=>"",
 "button"=>"",
 "action"=>"show",
 "controller"=>"search"}
```

Obviously it doesn't make sense to execute the search for the first request, since that one doesn't have a scope or a search string.

Please review this carefully since this modifies the search and may break things i can't think of.

@dzaporozhets While this fixes the root cause for the failing test, I think we should keep your fix in as a failsafe. What do you think of this?

See merge request !302

app/controllers/search_controller.rb

@@ -2,12 +2,14 @@ class SearchController < ApplicationController
   include SearchHelper
 
   def show
+    return if params[:search].nil? || params[:search].blank?
     @project = Project.find_by(id: params[:project_id]) if params[:project_id].present?
     @group = Group.find_by(id: params[:group_id]) if params[:group_id].present?
     @scope = params[:scope]
     @show_snippets = params[:snippets].eql? 'true'
 
-    @search_results = if @project
+    @search_results = 
+      if @project
         return access_denied! unless can?(current_user, :download_code, @project)
 
         unless %w(blobs notes issues merge_requests wiki_blobs).
@@ -26,10 +28,8 @@ class SearchController < ApplicationController
         unless %w(projects issues merge_requests).include?(@scope)
           @scope = 'projects'
         end
-
         Search::GlobalService.new(current_user, params).execute
       end
-
     @objects = @search_results.objects(@scope, params[:page])
   end