Merge branch 'search-wiki-keyword' into 'master'

Prevent 500 error on search results if description contains relative link

Bug: If I add relative link to comment or description and search for it - I get 500 error on search page.

Reason for this is that we use `@repository` variable. But for pages like search it does not assigned.
In future we should avoid using such variables. Especially in markdown parser that can be used on different pages

Fixes #1601

See merge request !1111

app/helpers/gitlab_markdown_helper.rb

@@ -73,7 +73,12 @@ module GitlabMarkdownHelper
     paths.uniq.each do |file_path|
       # If project does not have repository
       # its nothing to rebuild
-      if @repository.exists? && !@repository.empty?
+      #
+      # TODO: pass project variable to markdown helper instead of using
+      # instance variable. Right now it generates invalid path for pages out
+      # of project scope. Example: search results where can be rendered markdown
+      # from different projects
+      if @repository && @repository.exists? && !@repository.empty?
         new_path = rebuild_path(file_path)
         # Finds quoted path so we don't replace other mentions of the string
         # eg. "doc/api" will be replaced and "/home/doc/api/text" won't