Don't allow editing of title and category of an archived topic

lib/guardian.rb

@@ -259,7 +259,7 @@ class Guardian
   end
 
   def can_edit_topic?(topic)
-    is_staff? || is_my_own?(topic)
+    !topic.archived && (is_staff? || is_my_own?(topic))
   end
 
   # Deleting Methods

spec/components/guardian_spec.rb

@@ -456,12 +456,24 @@ describe Guardian do
         Guardian.new(coding_horror).can_edit?(topic).should be_false
       end
 
-      it 'returns true as a moderator' do
-        Guardian.new(moderator).can_edit?(topic).should be_true
+      context 'not archived' do
+        it 'returns true as a moderator' do
+          Guardian.new(moderator).can_edit?(topic).should be_true
+        end
+
+        it 'returns true as an admin' do
+          Guardian.new(admin).can_edit?(topic).should be_true
+        end
       end
 
-      it 'returns true as an admin' do
-        Guardian.new(admin).can_edit?(topic).should be_true
+      context 'archived' do
+        it 'returns false as a moderator' do
+          Guardian.new(moderator).can_edit?(build(:topic, user: user, archived: true)).should be_false
+        end
+
+        it 'returns false as an admin' do
+          Guardian.new(admin).can_edit?(build(:topic, user: user, archived: true)).should be_false
+        end
       end
     end