Create connection with PG.connect

* Add rescue block to match upstream

https://github.com/rails/rails/blob/6-0-stable/activerecord/lib/active_record/connection_adapters/postgresql_adapter.rb#L33

lib/active_record/connection_adapters/postgis/create_connection.rb

@@ -31,13 +31,18 @@ def postgis_connection(config)
         conn_params[:user] = conn_params.delete(:username) if conn_params[:username]
         conn_params[:dbname] = conn_params.delete(:database) if conn_params[:database]
 
-        # Forward only valid config params to PGconn.connect.
+        # Forward only valid config params to PG.connect
         valid_conn_param_keys = PG::Connection.conndefaults_hash.keys + [:requiressl]
         conn_params.slice!(*valid_conn_param_keys)
 
-        # The postgres drivers don't allow the creation of an unconnected PGconn object,
-        # so just pass a nil connection object for the time being.
-        ConnectionAdapters::PostGISAdapter.new(nil, logger, conn_params, config)
+        conn = PG.connect(conn_params)
+        ConnectionAdapters::PostGISAdapter.new(conn, logger, conn_params, config)
+      rescue ::PG::Error => error
+        if error.message.include?(conn_params[:dbname])
+          raise ActiveRecord::NoDatabaseError
+        else
+          raise
+        end
       end
 
     end