[FE] Comment field shown on POI detail page even though it's empty

[1000miles]

This is a follow-up ticket of #606 (comment).

Steps to reproduce:

• I am on https://wheelmap.org/en/nodes/-452678133
• I click on edit button
• I sign into osm and I am redirected to the wheelmap POI
• I can see there is no comment yet for the wheelmap:description tag
• I click on save button without adding/changing anything in the comment field

=> actual behavior: empty comment field is visible
=> expected behavior: if comment field is empty do not show on wheelmap POI

Needs clarification:

• If a wheelmap POI has a previous comment and I remove that comment (by emptying the comment field), should my edit be considered as a total removal of the whole comment or as an update and therefore being saved/synced to osm and back?

Possible solution:

• Consider all changes as updates and save them in the backend but do not show the comment field in the front-end if it is empty