Clicking *Comment* button without any body or attachment results incorrectly in webpage refresh

### Description

Related to #177.

At least on Codeberg.

### Gitea Version

Not read.

### Can you reproduce the bug on the Gitea demo site?

Yes

### Log Gist

_No response_

### Screenshots

_No response_

### Git Version

_No response_

### Operating System

_No response_

### How are you running Gitea?

Not read.

### Database

None