MXS-2015: Always check for error responses

As a JSON object can never start with the ERR prefix, it is safe to check
it for all requests. Also fixed the missing newline in the avrorouter
error message.

connectors/cdc-connector/cdc_connector.cpp

@@ -584,7 +584,7 @@ bool Connection::read_row(std::string& dest)
         m_buf_ptr = m_buffer.begin();
     }
 
-    if (!m_connected && is_error(dest.c_str()))
+    if (is_error(dest.c_str()))
     {
         rval = false;
     }