Fixed incorrect call count upon message sending failure when making call

[sauwming]

To fix #4384.

If pjsip_inv_send_msg() fails, the call count is not reverted.

/* Must increment call counter now */
++pjsua_var.call_cnt;

/* Send initial INVITE: */
status = pjsip_inv_send_msg(inv, tdata);
if (status != PJ_SUCCESS) {
    cb_called = PJ_TRUE;

    /* Upon failure to send first request, the invite
     * session would have been cleared.
     */
    call->inv = inv = NULL;
    goto on_error;
}

[Copilot]

Pull Request Overview

This PR fixes a bug where the call counter was incorrectly left incremented when pjsip_inv_send_msg() failed, potentially causing call count mismatches.

• Reverts the earlier increment of the call counter by decrementing it upon failure.
• Separates the nullification of the invite pointer from the resetting of the local variable.

Comments suppressed due to low confidence (2)

pjsip/src/pjsua-lib/pjsua_call.c:580

• Reverting the call count increment via a direct decrement is appropriate; however, please ensure that pjsua_var.call_cnt does not become negative in any failure scenarios.

--pjsua_var.call_cnt;

pjsip/src/pjsua-lib/pjsua_call.c:579

• Removing the assignment 'inv = NULL' is acceptable as long as subsequent error handling relies solely on call->inv. Please verify that no other cleanup logic depends on the local variable 'inv'.

call->inv = NULL;

[nanangizz]

Some/most paths of pjsip_inv_send_msg() failure seem to invoke on_state_changed(PJSIP_INV_STATE_DISCONNECTED) which eventually will decrement the 'pjsua_var.call_cnt', so after this patch, the call counter may be decremented twice?