inner html error reminder is not useful if we set the player size smaller than 640*480

[fangxian]

In the vxgplayer.js，showGlobalErrorMessage function will not display the error message in the proper location in the player if we set the player size smaller than 640 * 480. For example if we set the player 240*180, we will not be able to see the error message which is produced by showGlobalErrorMessage.