fix leak of unmuted score when escaping out of what-if edit

This adds GradeSummaryAssignmentPresenter#original_points, which won't
share the published_score with the grade_summary page if the
assignment is muted or the submission is nil.

fixes CNVS-36928

test plan:
 - Have a course with a teacher, a student, and an assignment.
 - As the teacher, mute the assignment and grade the student
 - As the student, visit the grade summary page.
 - Select the muted icon to go into what-if editing mode, but hit
   escape without entering any data.
 - Note that the total score remains the same as it originally was
 - Select the muted icon and enter a what-if score. Rever that score.
 - Note that the total score the same as it originally was

Change-Id: I9a30dcd09e2c7c10d4c70a1fdea7a764db5a127c
Reviewed-on: https://gerrit.instructure.com/111925
Reviewed-by: Cody Cutrer <cody@instructure.com>
Tested-by: Jenkins
Reviewed-by: Neil Gupta <ngupta@instructure.com>
QA-Review: Anju Reddy <areddy@instructure.com>
Product-Review: Keith T. Garner <kgarner@instructure.com>

app/presenters/grade_summary_assignment_presenter.rb

@@ -70,6 +70,10 @@ class GradeSummaryAssignmentPresenter
     assignment.muted? || submission.nil?
   end
 
+  def original_points
+    has_no_score_display? ? '' : submission.published_score
+  end
+
   def unchangeable?
     (!@summary.editable? || assignment.special_class)
   end

app/views/gradebooks/grade_summary.html.erb

@@ -243,7 +243,7 @@
           <div style="display: none;">
             <!-- Store the original points so we don't need to parse and guess at locale -->
             <span class="original_points">
-              <%= submission&.published_score %>
+              <%= assignment_presenter.original_points %>
             </span>
             <!-- Store the original score so that we can retrieve it after any "What-If" calculations -->
             <span class="original_score">

spec/presenters/grade_summary_assignment_presenter_spec.rb

@@ -81,4 +81,20 @@ describe GradeSummaryAssignmentPresenter do
       end
     end
   end
+
+  context "#original_points" do
+    it "returns an empty string when assignment is muted" do
+      @assignment.muted = true
+      expect(presenter.original_points).to eq ''
+    end
+
+    it "returns an empty string when submission is nil" do
+      test_presenter = GradeSummaryAssignmentPresenter.new(summary, @student, @assignment, nil)
+      expect(test_presenter.original_points).to eq ''
+    end
+
+    it "returns the published score" do
+      expect(presenter.original_points).to eq @submission.published_score
+    end
+  end
 end