xhr state might change in subsequence call on this function

[namgk]

This function here

https://github.com/Iperity/node-strophe/blob/c06c157b1b97f3365a2571d48a9c0fed221e0a34/strophe.js#L2218

is triggered also by the setTimeout function. In that case, the xhr state might change, sometime result in the following error:

Error: INVALID_STATE_ERR: connection must be opened before send() is called