Fix NPE when context isn't available

Author: BlooJeans

android/src/main/java/io/fullstack/firestack/FirestackUtils.java

@@ -40,7 +40,7 @@ public static void todoNote(final String tag, final String name, final Callback
   public static void sendEvent(final ReactContext context,
                                final String eventName,
                                final WritableMap params) {
-    if (context.hasActiveCatalystInstance()) {
+    if (context != null && context.hasActiveCatalystInstance()) {
       context
           .getJSModule(DeviceEventManagerModule.RCTDeviceEventEmitter.class)
           .emit(eventName, params);