Fix `Wreorder-ctor` warning
```
spdlog/pattern_formatter-inl.h:1028:7: error: field 'custom_handlers_' will be initialized after field 'need_localtime_' [-Werror,-Wreorder-ctor]
, custom_handlers_(std::move(custom_user_flags))
^
```
Move the initialization of `need_localtime_(true)` right after `pattern_time_type_` as expected.