[sr-dev] [kamailio/kamailio] cancel_branch("this") not working (#1620)

Need add _tmx_tmb.prepare_to_cancel(t, &cancel_data.cancel_bitmap, 0);

into function static int t_cancel_branches_helper(sip_msg_t* msg, int n)

at case of 2( "this")

proposed changes: ```

case 2: /* prepare cancel for current branch (idx) */ if(msg->first_line.u.reply.statuscode>=200) break; cancel_data.cancel_bitmap = 1<<idx; + _tmx_tmb.prepare_to_cancel(t, &cancel_data.cancel_bitmap, 0); break; ```

### Additional Information

kamailio version 4.* to 5.*

``` ```

Without this it can't cancel "this" transaction.

Rare case due to low use of "this".