Notifcations that replace another still 'stack'

I'm using dustify in a volume changing script. If you replace the id of a notification it still acts like its stacking even though you are replacing it.
relavent dunstrc option
```
[global]
stack_duplicates = yes
```
When stack_duplicates = no the behavior does not exist

Example command that duplicates this.
```
dunstify -p -r 8 "Hello World" "Hello o/"
```

Moving the replace id logic to before the stack_duplicates check fixes this