Change percent_complete rescue value from 100 to 0

The percent_complete method returns a value of 100 when a
ZeroDivisionError occurs. That seems like a very strange default for an
error case, and results in a bug when a milestone has no corresponding
issues (new, empty milestones show 100% completion). This commit changes
the rescue value to 0, and subsequently fixes #1656, which reported this
problem.

CHANGELOG

@@ -11,6 +11,7 @@ v 7.12.0 (unreleased)
   - Update Asciidoctor gem to version 1.5.2. (Jakub Jirutka)
   - Fix resolving of relative links to repository files in AsciiDoc documents. (Jakub Jirutka)
   - Use the user list from the target project in a merge request (Stan Hu)
+  - Fix new/empty milestones showing 100% completion value (Jonah Bishop)
 
 v 7.11.2
   - no changes

app/models/group_milestone.rb

@@ -44,7 +44,7 @@ class GroupMilestone
   def percent_complete
     ((closed_items_count * 100) / total_items_count).abs
   rescue ZeroDivisionError
-    100
+    0
   end
 
   def state

app/models/milestone.rb

@@ -66,7 +66,7 @@ class Milestone < ActiveRecord::Base
   def percent_complete
     ((closed_items_count * 100) / total_items_count).abs
   rescue ZeroDivisionError
-    100
+    0
   end
 
   def expires_at

spec/models/milestone_spec.rb

@@ -47,7 +47,7 @@ describe Milestone do
 
     it "should recover from dividing by zero" do
       expect(milestone.issues).to receive(:count).and_return(0)
-      expect(milestone.percent_complete).to eq(100)
+      expect(milestone.percent_complete).to eq(0)
     end
   end