Fix bugs when discussion visible in wrong project

Because notes scope was not limited by project in
MergeRequest#mr_and_commit_notes it causes comments from project A
appears in discussions for MR in project B.

app/models/merge_request.rb

@@ -222,7 +222,11 @@ class MergeRequest < ActiveRecord::Base
   def mr_and_commit_notes
     commit_ids = commits.map(&:id)
-    Note.where("(noteable_type = 'MergeRequest' AND noteable_id = :mr_id) OR (noteable_type = 'Commit' AND commit_id IN (:commit_ids))", mr_id: id, commit_ids: commit_ids)
+    project.notes.where(
+      "(noteable_type = 'MergeRequest' AND noteable_id = :mr_id) OR (noteable_type = 'Commit' AND commit_id IN (:commit_ids))",
+      mr_id: id,
+      commit_ids: commit_ids
+    )
   end
   # Returns the raw diff for this merge request