title: adapter.getBluetoothLeScanner() returns null on some Android 6.0 devices
body: <p>My App works with BLE devices and searches them in the following way (API 21+):</p>
  
  <pre><code>adapter.getBluetoothLeScanner().startScan(filters, scanSettings, this);
  </code></pre>
  
  <p>It works just perfect for most devices (f.e. Samsung) but returns <code>null</code> on some LGE and HTC devices (with Android 6.0) and crashes:</p>
  
  <blockquote>
    <p>Caused by java.lang.NullPointerException: Attempt to invoke virtual method 'void android.bluetooth.le.BluetoothLeScanner.startScan(java.util.List, android.bluetooth.le.ScanSettings, android.bluetooth.le.ScanCallback)' on a null object reference</p>
  </blockquote>
  
  <p>The app is targeted to pre-marshmallow android so the premissions are (should be) granted.</p>