Fixed 'boolean android.database.Cursor.moveToNext()' on a null object reference error

Closes #259
Closes #255

Author: MoOx

android/src/main/java/com/calendarevents/RNCalendarEvents.java

@@ -806,7 +806,7 @@ private void createAttendeesForEvent(ContentResolver resolver, int eventID, Read
         Cursor cursor = CalendarContract.Attendees.query(resolver, eventID, new String[] {
                 CalendarContract.Attendees._ID
         });
-
+        
         while (cursor.moveToNext()) {
             long attendeeId = cursor.getLong(0);
             Uri attendeeUri = ContentUris.withAppendedId(CalendarContract.Attendees.CONTENT_URI, attendeeId);
@@ -1135,12 +1135,13 @@ private WritableNativeMap serializeEvent(Cursor cursor) {
     private WritableNativeArray serializeEventCalendars(Cursor cursor) {
         WritableNativeArray results = new WritableNativeArray();
 
-        while (cursor.moveToNext()) {
-            results.pushMap(serializeEventCalendar(cursor));
+        if (cursor != null) {
+            while (cursor.moveToNext()) {
+                results.pushMap(serializeEventCalendar(cursor));
+            }
+            cursor.close();
         }
 
-        cursor.close();
-
         return results;
     }