FIX: Permission issues when editing topics

If a user can't create a topic in a category, they should'be be
able to edit topics.

lib/guardian/topic_guardian.rb

@@ -29,7 +29,9 @@ module TopicGuardian
   def can_edit_topic?(topic)
     return false if Discourse.static_doc_topic_ids.include?(topic.id) && !is_admin?
     return false unless can_see?(topic)
-    return true if is_staff? || (!topic.private_message? && user.has_trust_level?(TrustLevel[3]))
+    return true if is_staff?
+    return true if (!topic.private_message? && user.has_trust_level?(TrustLevel[3]) && can_create_post?(topic))
+
     return false if topic.archived
     is_my_own?(topic) && !topic.edit_time_limit_expired?
   end

spec/components/guardian_spec.rb

@@ -530,7 +530,6 @@ describe Guardian do
         category.save
 
         expect(Guardian.new(topic.user).can_create?(Post, topic)).to be_falsey
-
       end
 
       it "is false when not logged in" do
@@ -889,6 +888,13 @@ describe Guardian do
         it 'returns true at trust level 3' do
           expect(Guardian.new(trust_level_3).can_edit?(topic)).to eq(true)
         end
+
+        it "returns false when the category is read only" do
+          topic.category.set_permissions(everyone: :readonly)
+          topic.category.save
+
+          expect(Guardian.new(trust_level_3).can_edit?(topic)).to eq(false)
+        end
       end
 
       context 'private message' do