fix: use m_whiteList.data() - operator[] on an empty vector is UB

After erasing the last whitelist entry, &m_whiteList[0] indexes an empty
vector before ble_gap_wl_set(..., 0). data() is well-defined for empty
vectors; same change applied to the whiteListAdd call site for consistency.

Author: sanastasiou

src/NimBLEDevice.cpp

@@ -728,7 +728,7 @@ bool NimBLEDevice::onWhiteList(const NimBLEAddress& address) {
 bool NimBLEDevice::whiteListAdd(const NimBLEAddress& address) {
     if (!NimBLEDevice::onWhiteList(address)) {
         m_whiteList.push_back(address);
-        int rc = ble_gap_wl_set(reinterpret_cast<ble_addr_t*>(&m_whiteList[0]), m_whiteList.size());
+        int rc = ble_gap_wl_set(reinterpret_cast<ble_addr_t*>(m_whiteList.data()), m_whiteList.size());
         if (rc != 0) {
             NIMBLE_LOGE(LOG_TAG, "Failed adding to whitelist rc=%d", rc);
             m_whiteList.pop_back();
@@ -748,7 +748,7 @@ bool NimBLEDevice::whiteListRemove(const NimBLEAddress& address) {
     for (auto it = m_whiteList.begin(); it < m_whiteList.end(); ++it) {
         if (*it == address) {
             m_whiteList.erase(it);
-            int rc = ble_gap_wl_set(reinterpret_cast<ble_addr_t*>(&m_whiteList[0]), m_whiteList.size());
+            int rc = ble_gap_wl_set(reinterpret_cast<ble_addr_t*>(m_whiteList.data()), m_whiteList.size());
             if (rc != 0) {
                 m_whiteList.push_back(address);
                 NIMBLE_LOGE(LOG_TAG, "Failed removing from whitelist rc=%d", rc);