Improve cleanup in BLEClient (#4742)

- Remove client from the list of devices in case registration fails
- Filter other events not related to registration during registration phase
- Cleanup if connect fails
- Reset if after disconnect
- Disconnect callback *after* cleanup is done so object can be deleted

This fixes some of the issues I had like:
- `BLEClient::connect` hangs up and never recovered because registration failed
- `BLEClient` could not be deleted after disconnect or deletion creating ghost events https://github.com/espressif/arduino-esp32/issues/4047
- `BLEClient` could not be properly reused after a connection was attempted (successful or not) 

* Cleanup in case of registration and connect failure.
Cleanup before calling disconnect callback for safe delete.
Reject other events during registration.
Adresses #4047, #4055

* Clear if after unregister #4047

libraries/BLE/src/BLEClient.cpp

@@ -110,7 +110,17 @@ bool BLEClient::connect(BLEAddress address, esp_ble_addr_type_t type) {
 		return false;
 	}
 
-	m_semaphoreRegEvt.wait("connect");
+	uint32_t rc = m_semaphoreRegEvt.wait("connect");
+
+	if (rc != ESP_GATT_OK) {
+		// fixes ESP_GATT_NO_RESOURCES error mostly
+		log_e("esp_ble_gattc_app_register_error: rc=%d", rc);
+		BLEDevice::removePeerDevice(m_appId, true);
+		// not sure if this is needed here
+		// esp_ble_gattc_app_unregister(m_gattc_if);
+		// m_gattc_if = ESP_GATT_IF_NONE;
+		return false;
+	}
 
 	m_peerAddress = address;
 
@@ -128,7 +138,13 @@ bool BLEClient::connect(BLEAddress address, esp_ble_addr_type_t type) {
 		return false;
 	}
 
-	uint32_t rc = m_semaphoreOpenEvt.wait("connect");   // Wait for the connection to complete.
+	rc = m_semaphoreOpenEvt.wait("connect");   // Wait for the connection to complete.
+	// check the status of the connection and cleanup in case of failure
+	if (rc != ESP_GATT_OK) {
+		BLEDevice::removePeerDevice(m_appId, true);
+		esp_ble_gattc_app_unregister(m_gattc_if);
+		m_gattc_if = ESP_GATT_IF_NONE;
+	}
 	log_v("<< connect(), rc=%d", rc==ESP_GATT_OK);
 	return rc == ESP_GATT_OK;
 } // connect
@@ -160,6 +176,11 @@ void BLEClient::gattClientEventHandler(
 	log_d("gattClientEventHandler [esp_gatt_if: %d] ... %s",
 		gattc_if, BLEUtils::gattClientEventTypeToString(event).c_str());
 
+	// it is possible to receive events from other connections while waiting for registration
+	if (m_gattc_if == ESP_GATT_IF_NONE && event != ESP_GATTC_REG_EVT) {
+		return;
+	}
+
 	// Execute handler code based on the type of event received.
 	switch(event) {
 
@@ -184,15 +205,17 @@ void BLEClient::gattClientEventHandler(
 				if (evtParam->disconnect.conn_id != getConnId()) break;
 				// If we receive a disconnect event, set the class flag that indicates that we are
 				// no longer connected.
-				if (m_isConnected && m_pClientCallbacks != nullptr) {
-					m_pClientCallbacks->onDisconnect(this);
-				}
+				bool m_wasConnected = m_isConnected;
 				m_isConnected = false;
 				esp_ble_gattc_app_unregister(m_gattc_if);
+				m_gattc_if = ESP_GATT_IF_NONE;
 				m_semaphoreOpenEvt.give(ESP_GATT_IF_NONE);
 				m_semaphoreRssiCmplEvt.give();
 				m_semaphoreSearchCmplEvt.give(1);
 				BLEDevice::removePeerDevice(m_appId, true);
+				if (m_wasConnected && m_pClientCallbacks != nullptr) {
+					m_pClientCallbacks->onDisconnect(this);
+				}
 				break;
 		} // ESP_GATTC_DISCONNECT_EVT
 
@@ -228,7 +251,8 @@ void BLEClient::gattClientEventHandler(
 		//
 		case ESP_GATTC_REG_EVT: {
 			m_gattc_if = gattc_if;
-			m_semaphoreRegEvt.give();
+			// pass on the registration status result, in case of failure
+			m_semaphoreRegEvt.give(evtParam->reg.status);
 			break;
 		} // ESP_GATTC_REG_EVT