Added proper SQL engine termination

Since the SQL engine is initialized in _SQLAllocEnv, the engine should be also terminated in SQLFreeEnv.

src/odbc/odbc.c

@@ -1300,6 +1300,7 @@ static SQLRETURN SQL_API _SQLFreeEnv(
 		return SQL_ERROR;
 	}
 	g_ptr_array_free(env->connections, TRUE);
+	mdb_sql_exit(env->sql);
 	g_free(env);
 
 	return SQL_SUCCESS;