Fix CI segfault and address PR #480 review comments

  - Fix unit test SIGSEGV on macOS: call MqttProps_Init/ShutDown for v5
    static property pool semaphore initialization
  - Use xfer instead of client->write.len for tx_buf clearing (write.len
    is zeroed by MqttWriteStop before the XMEMSET)
  - Free decoded v5 props in roundtrip test to prevent pool exhaustion
  - Remove unused T24_PLUS_RC/T24_HASH_RC variables in broker.test
  - Change TLS credential warning guard from WOLFMQTT_DEBUG_CLIENT to
    DEBUG_WOLFMQTT for broader coverage

Author: aidangarske

scripts/broker.test

@@ -940,11 +940,9 @@ wait_for_file "${TMP_DIR}/t24_sub.ready" 5
 # Attempt to PUBLISH with '+' in the topic name (must be rejected by broker)
 ./$pub_bin -T -h 127.0.0.1 -p $port -n "test/+/card" -m "bad_wildcard_plus" \
     >"${TMP_DIR}/t24_pub_plus.log" 2>&1
-T24_PLUS_RC=$?
 # Attempt to PUBLISH with '#' in the topic name (must be rejected by broker)
 ./$pub_bin -T -h 127.0.0.1 -p $port -n "test/#" -m "bad_wildcard_hash" \
     >"${TMP_DIR}/t24_pub_hash.log" 2>&1
-T24_HASH_RC=$?
 sleep 0.3
 kill $T24_SUB_PID 2>/dev/null
 wait $T24_SUB_PID 2>/dev/null || true

src/mqtt_client.c

@@ -1664,7 +1664,7 @@ int MqttClient_Connect(MqttClient *client, MqttConnect *mc_connect)
     }
 
     if (mc_connect->stat.write == MQTT_MSG_BEGIN) {
-    #ifdef WOLFMQTT_DEBUG_CLIENT
+    #ifdef DEBUG_WOLFMQTT
         /* Warn if credentials are being sent without TLS */
         if ((mc_connect->username != NULL || mc_connect->password != NULL) &&
             !(MqttClient_Flags(client, 0, 0) & MQTT_CLIENT_FLAG_IS_TLS)) {
@@ -1728,8 +1728,9 @@ int MqttClient_Connect(MqttClient *client, MqttConnect *mc_connect)
     #endif
         MqttWriteStop(client, &mc_connect->stat);
 
-        /* Clear tx_buf to remove any plaintext credentials from memory */
-        XMEMSET(client->tx_buf, 0, client->write.len);
+        /* Clear tx_buf to remove any plaintext credentials from memory.
+         * Use xfer (saved before MqttWriteStop zeroes client->write) */
+        XMEMSET(client->tx_buf, 0, xfer);
 
         if (rc != xfer) {
             MqttClient_CancelMessage(client, (MqttObject*)mc_connect);

tests/unit_test.c

@@ -352,6 +352,10 @@ static void test_publish_resp_v5_roundtrip(void)
           "v5 PUBACK SUCCESS+props: packet_id roundtrip");
     CHECK(dec.reason_code == MQTT_REASON_SUCCESS,
           "v5 PUBACK SUCCESS+props: reason_code roundtrip");
+    if (dec.props) {
+        MqttProps_Free(dec.props);
+        dec.props = NULL;
+    }
 
     /* Case: reason_code=non-SUCCESS, props=NULL (baseline, should work) */
     XMEMSET(&enc, 0, sizeof(enc));
@@ -584,6 +588,10 @@ int main(int argc, char** argv)
 
     PRINTF("wolfMQTT Unit Tests");
 
+#ifdef WOLFMQTT_V5
+    MqttProps_Init();
+#endif
+
     test_vbi();
     test_encode_publish();
     test_decode_connack();
@@ -596,6 +604,7 @@ int main(int argc, char** argv)
     test_decode_unsuback();
 #ifdef WOLFMQTT_V5
     test_publish_resp_v5_roundtrip();
+    MqttProps_ShutDown();
 #endif
 
     PRINTF("=== Results: %d/%d passed ===",