Fix Rainbow Database.Dispose() so that it never throws and not overrides the active exception (if any)

Author: dmytro-gokun

Dapper.Rainbow/Database.cs

@@ -466,13 +466,10 @@ public SqlMapper.GridReader QueryMultiple(string sql, dynamic param = null, IDbT
         /// </summary>
         public void Dispose()
         {
-            if (_connection.State != ConnectionState.Closed)
-            {
-                _transaction?.Rollback();
-
-                _connection.Close();
-                _connection = null;
-            }
+            var connection = _connection;
+            _connection = null;
+            _transaction = null;
+            connection?.Close();
         }
     }
 }