Fix inconsistent convention on when to destroy tx_data about pjproject HOT 1 CLOSED

This is true and the situation is even worse than described with the inconsistency even happening for similar APIs of the same component, for example:
pjsip_endpt_send_response() does the decrement only upon PJ_SUCCESS, but for some reason,
pjsip_endpt_send_request() will always decrement the counter, and pjsip_endpt_send_request_stateless() only upon PJ_SUCCESS.

Here is a summary of other APIs that I check (the list may not be complete):
pjsip_transport_send() PJ_SUCCESS only
pjsip_inv_send_msg() always
pjsip_dlg_send_mg() always
pjsip_tsx_send_msg() PJ_SUCCESS only

Unfortunately I think it's already too late to change this since it will introduce significant backward compatibility.

When I modified the behavior such as pjsip_tsx_send_msg() to always decrement the counter and tested it here, it will introduce crashes in pjsip test and the application, due to double destruction. The only possible workaround is to use a timer to create a delayed destruction. Still, it's quite a hackish workaround and is not guaranteed to completely eliminate the issue.

Conclusion: the issue is valid and it's not ideal, but won't/can't fix.

from pjproject.