postGradesInit() no longer dependent on @sections_enabled?

fixes SIS-323

TestPlan:
 - Enable Post Grades in account
 - Enable Post Grades in Course
 - verify Post Grades button renders in tabs
 - Post Grades should show dialog window when clicked.

Change-Id: If435b95bbdaf8a5d23ec803079934a631f7ed282
Reviewed-on: https://gerrit.instructure.com/36160
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Duane Johnson <duane@instructure.com>
Product-Review: Duane Johnson <duane@instructure.com>
Reviewed-by: Simon Williams <simon@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>

Author: Eric Adams

app/coffeescripts/gradebook2/Gradebook.coffee

@@ -757,7 +757,6 @@ define [
         sections: @sectionList(),
         currentSection: @sectionToShow)
       @sectionMenu.render()
-      @initPostGrades()
 
     updateCurrentSection: (section, author) =>
       @sectionToShow = section
@@ -801,6 +800,8 @@ define [
       @userFilter = new InputFilterView el: '.gradebook_filter input'
       @userFilter.on 'input', @onUserFilterInput
 
+      @initPostGrades()
+
       @renderTotalHeader()
 
     studentNamesToggle: (e) =>