add check for battery status not availlable, return default value instead (#521)

Author: tobrun

mapbox/libandroid-telemetry/src/main/java/com/mapbox/services/android/telemetry/MapboxTelemetry.java

@@ -51,6 +51,7 @@
 public class MapboxTelemetry implements Callback, LocationEngineListener {
 
   private static final String LOG_TAG = MapboxTelemetry.class.getSimpleName();
+  private static final int UNAVAILABLE_BATTERY_LEVEL = 100;
 
   private static MapboxTelemetry instance;
 
@@ -241,9 +242,13 @@ private void registerBatteryUpdates() {
   }
 
   private int getBatteryLevel() {
-    int level = batteryStatus.getIntExtra(BatteryManager.EXTRA_LEVEL, -1);
-    int scale = batteryStatus.getIntExtra(BatteryManager.EXTRA_SCALE, -1);
-    return Math.round((level / (float) scale) * 100);
+    if (batteryStatus != null) {
+      int level = batteryStatus.getIntExtra(BatteryManager.EXTRA_LEVEL, -1);
+      int scale = batteryStatus.getIntExtra(BatteryManager.EXTRA_SCALE, -1);
+      return Math.round((level / (float) scale) * 100);
+    } else {
+      return UNAVAILABLE_BATTERY_LEVEL;
+    }
   }
 
   /**