Fix prev events not being hashed and signed during room creation.

priv/repo/migrations/20210818133912_add_fields_to_events.exs

@@ -0,0 +1,11 @@
+defmodule MatrixServer.Repo.Migrations.AddFieldsToEvents do
+  use Ecto.Migration
+
+  def change do
+    alter table(:events) do
+      add :unsigned, :map, default: %{}, null: true
+      add :hashes, :map, null: false
+      add :signatures, :map, null: false
+    end
+  end
+end