Fixed dialog event Coverity warnings

[sauwming]

Re #3754 , Coverity yields a couple of warnings:

>>>     CID 1533986:  Concurrent data access violations  (MISSING_LOCK)
>>>     Accessing "dlgev->status" without holding lock "pj_mutex_t.mutex". Elsewhere, "pjsip_dlg_event.status" is written to with "pj_mutex_t.mutex" held 1 out of 1 times.
567             for (i=0; i<dlgev->status.info_cnt; ++i) {
568                 dlgev->[status.info](http://status.info/)[i].dialog_node = NULL;

353             info->dialog_info_state.ptr = info->buf_ + total;
>>>     CID 1533985:    (OVERRUN)
>>>     Overrunning array of 1024 bytes at byte offset 1024 by dereferencing pointer "info->dialog_info_state.ptr".