make singleton

SQLite.cs

@@ -9,9 +9,15 @@ namespace VRCX
 {
     public class SQLite
     {
+        public static SQLite Instance { get; private set; }
         private static readonly ReaderWriterLockSlim m_Lock = new ReaderWriterLockSlim();
         private static SQLiteConnection m_Connection;
 
+        static SQLite()
+        {
+            Instance = new SQLite();
+        }
+
         public static void Init()
         {
             m_Connection = new SQLiteConnection($"Data Source={Application.StartupPath}/VRCX.sqlite;Version=3");