fix: repeated label removed from file on change click bug

- When the modal was rendered it was incorrectly updating the fileList as the previousTags variable was undefined.
- The update function only ever applies a tag to a single file so the second file was not being tagged.
- Set the previousTags to the last state or the initialTags on first render
- Updates are checked but an update isn't applied as the previousTags = intialTags

editor.planx.uk/src/@planx/components/FileUploadAndLabel/Modal.tsx

@@ -147,7 +147,7 @@ const SelectMultiple = (props: SelectMultipleProps) => {
 
   const initialTags = getTagsForSlot(uploadedFile.id, fileList);
   const [tags, setTags] = useState<string[]>(initialTags);
-  const previousTags = usePrevious(tags);
+  const previousTags = usePrevious(tags) || initialTags;
   const [open, setOpen] = React.useState(false);
 
   const handleChange = (event: SelectChangeEvent<typeof tags>) => {