Don't complain if asset view score is undefined

Closes CNVS-10914

TEST PLAN
---- ----

I'm really not sure how to reproduce it. We need a student to have
accessed a quiz (viewed it) but the view score to also be nil and not 1
(or 0), then try to view the access report for that student.

Anyway, it's just a guard against nil-values, so the spec should be
sufficient.

Change-Id: Id1fbcb3a36745fb289be73f76c78f1d52656a3b7

app/models/asset_user_access.rb

@@ -185,10 +185,11 @@ class AssetUserAccess < ActiveRecord::Base
   def corrected_view_score
     deductible_points = 0
 
-    if %w[ quizzes ].include?(self.asset_group_code || '')
+    if 'quizzes' == self.asset_group_code
       deductible_points = self.participate_score || 0
     end
 
+    self.view_score ||= 0
     self.view_score -= deductible_points
   end
 

spec/models/asset_user_access_spec.rb

@@ -172,22 +172,27 @@ describe AssetUserAccess do
   end
 
   describe '#corrected_view_score' do
-    let(:access) { AssetUserAccess.new }
-
     it 'should deduct the participation score from the view score for a quiz' do
-      access.stubs(:view_score).returns(10)
-      access.stubs(:participate_score).returns(4)
-      access.stubs(:asset_group_code).returns('quizzes')
+      subject.view_score = 10
+      subject.participate_score = 4
+      subject.asset_group_code = 'quizzes'
 
-      access.corrected_view_score.should == 6
+      subject.corrected_view_score.should == 6
     end
 
     it 'should return the normal view score for anything but a quiz' do
-      access.stubs(:view_score).returns(10)
-      access.stubs(:participate_score).returns(4)
+      subject.view_score = 10
+      subject.participate_score = 4
 
-      access.corrected_view_score.should == 10
+      subject.corrected_view_score.should == 10
     end
 
+    it 'should not complain if there is no current score' do
+      subject.view_score = nil
+      subject.participate_score = 4
+      subject.stubs(:asset_group_code).returns('quizzes')
+
+      subject.corrected_view_score.should == -4
+    end
   end
 end