Fix race condition in BM2 notification handling

Apply the same race condition fix to BM2 that was applied to BM6.
Set m_taskHandle before calling subscribe() to ensure the callback
can properly use the task handle even if notifications arrive immediately.

Changes:
- Set m_taskHandle before subscribe() instead of after
- Clear m_taskHandle on subscription failure
- Matches pattern now used in BM6

This prevents the callback from exiting early due to m_taskHandle
being nullptr when notifications arrive very quickly after subscription.

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: 1technophile

main/gatewayBLEConnect.cpp

@@ -319,14 +319,15 @@ void BM2_connect::publishData() {
 
   if (pChar && pChar->canNotify()) {
     THEENGS_LOG_TRACE(F("Registering notification" CR));
+    m_taskHandle = xTaskGetCurrentTaskHandle();
     if (pChar->subscribe(true, std::bind(&BM2_connect::notifyCB, this,
                                          std::placeholders::_1, std::placeholders::_2,
                                          std::placeholders::_3, std::placeholders::_4))) {
-      m_taskHandle = xTaskGetCurrentTaskHandle();
       if (ulTaskNotifyTake(pdTRUE, pdMS_TO_TICKS(BLE_CNCT_TIMEOUT)) == pdFALSE) {
         m_taskHandle = nullptr;
       }
     } else {
+      m_taskHandle = nullptr;
       THEENGS_LOG_NOTICE(F("Failed registering notification" CR));
     }
   }