initialized mysql binder member is_null_vector

backends/mysql/src/mysql_parameter_binder.cpp

@@ -90,6 +90,7 @@ void bind_value(enum_field_types type, const char *value, size_t, MYSQL_BIND &bi
 
 mysql_parameter_binder::mysql_parameter_binder(size_t size)
 : bind_params_(size)
+, is_null_vector(size)
 , info_(size)
 {}