Only load autocomplete data when actually needed

Previously this would result in autocomplete data being loaded for every
page (e.g. the page showing all Git branches of a project).

app/assets/javascripts/gfm_auto_complete.js.coffee

@@ -68,12 +68,13 @@ GitLab.GfmAutoComplete =
             title:  sanitize(m.title)
             search: "#{m.iid} #{m.title}"
 
-    $.getJSON(@dataSource).done (data) ->
-      # load members
-      input.atwho 'load', '@', data.members
-      # load issues
-      input.atwho 'load', 'issues', data.issues
-      # load merge requests
-      input.atwho 'load', 'mergerequests', data.mergerequests
-      # load emojis
-      input.atwho 'load', ':', data.emojis
+    if @dataSource
+      $.getJSON(@dataSource).done (data) ->
+        # load members
+        input.atwho 'load', '@', data.members
+        # load issues
+        input.atwho 'load', 'issues', data.issues
+        # load merge requests
+        input.atwho 'load', 'mergerequests', data.mergerequests
+        # load emojis
+        input.atwho 'load', ':', data.emojis

app/views/layouts/_init_auto_complete.html.haml

 - project = @target_project || @project
-:javascript
-  GitLab.GfmAutoComplete.dataSource = "#{autocomplete_sources_namespace_project_path(project.namespace, project, type: @noteable.class, type_id: params[:id])}"
-  GitLab.GfmAutoComplete.setup();
+
+- if @noteable
+  :javascript
+    GitLab.GfmAutoComplete.dataSource = "#{autocomplete_sources_namespace_project_path(project.namespace, project, type: @noteable.class, type_id: params[:id])}"
+    GitLab.GfmAutoComplete.setup();