LE/Android: add consistency check in method called from Qt API

Call to includedServices() from Qt side after unexpected disconnection
leads to NullPointerException due to unchecked member access. Fix that!

Change-Id: Iae89801d7af86d5a3f34ebba9eb2ea12da252cd2
Reviewed-by: Alex Blasche <alexander.blasche@qt.io>

src/android/bluetooth/src/org/qtproject/qt5/android/bluetooth/QtBluetoothLE.java

@@ -839,6 +839,9 @@ public class QtBluetoothLE {
      */
     public String includedServices(String serviceUuid)
     {
+        if (mBluetoothGatt == null)
+            return null;
+
         UUID uuid;
         try {
             uuid = UUID.fromString(serviceUuid);