fix: Unexpected preview mode disabling and add authorization to view PreviewAutocomplete in navbar

This MR resolves two bugs:

• Preview Mode was being disabled when the Preview Autocomplete field was blank. This is expected when the user clicks the X button but not when manually typing (ex. backspacing to an empty value.) as it is interruptive.
• The PreviewAutocomplete on the navbar was able to be seen by all users. Added a Protected component around the navbar's PreviewAutocomplete.