Non-SVG image links don't link to intended website

[Eisfunke]

• Gitea version (or commit ref): Tested on 1.2.3 and 40bbc73
• Operating system: Tested on Ubuntu 16.04.5 LTS and Arch Linux
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  Seems down, so I can't check.

Description

When embedding an image with a link like this
[![test](https://img.shields.io/badge/test-yes-green.svg)](https://example.org)
in a markdown file in Gitea, it correctly shows as the image and links to the intended website.

Though when the linked image is not an svg, like this
[![test](https://img.shields.io/badge/test-no-red.png)](https://example.org)
it doesn't link to the intended website, but only to the image itself.

You can see it here: https://git.eisfunke.com/Eisfunke/test/src/branch/master/README.md

On Github it works: https://github.com/Eisfunke/test/blob/master/README.md

[mappu]

I can confirm this issue still affects 1.5.1.

Markdown content like [![](doc/image.thumb.png)](doc/image.png) creates a link to image.thumb.png, not image.png.