Avoid NPE when DeviceInfo is null

(when a notification comes in while we're connected, but not initialized yet)

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/miband/MiBandSupport.java

@@ -171,6 +171,10 @@ public class MiBandSupport extends AbstractBTLEDeviceSupport {
     }
 
     private NotificationStrategy getNotificationStrategy() {
+        if (mDeviceInfo == null) {
+            // not initialized yet?
+            return new NoNotifcationStrategy();
+        }
         if (mDeviceInfo.getFirmwareVersion() < MiBandFWHelper.FW_16779790) {
             return new V1NotificationStrategy(this);
         } else {

app/src/main/java/nodomain/freeyourgadget/gadgetbridge/service/devices/miband/NoNotifcationStrategy.java

@@ -0,0 +1,25 @@
+package nodomain.freeyourgadget.gadgetbridge.service.devices.miband;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+import nodomain.freeyourgadget.gadgetbridge.devices.miband.VibrationProfile;
+import nodomain.freeyourgadget.gadgetbridge.service.btle.BtLEAction;
+import nodomain.freeyourgadget.gadgetbridge.service.btle.TransactionBuilder;
+
+/**
+ * Does not do anything.
+ */
+public class NoNotifcationStrategy implements NotificationStrategy {
+    private static final Logger LOG = LoggerFactory.getLogger(NoNotifcationStrategy.class);
+
+    @Override
+    public void sendDefaultNotification(TransactionBuilder builder, BtLEAction extraAction) {
+        LOG.info("dummy notification stragegy: default notification");
+    }
+
+    @Override
+    public void sendCustomNotification(VibrationProfile vibrationProfile, int flashTimes, int flashColour, int originalColour, long flashDuration, BtLEAction extraAction, TransactionBuilder builder) {
+        LOG.info("dummy notification stragegy: custom notification");
+    }
+}