The use of dash (-) in repository names breaks cross-referencing in issues

@lafriks

Gitea version (or commit ref): 82a7b02
Git version: ?
Operating system: irrelevant
Database (use [x]): irrelevant
Can you reproduce the bug at https://try.gitea.io:
- Yes: see below
- No
- Not relevant

Description

When you try to cross-reference an issue in a repository whose name contains a dash (`-˙ symbol), the automatic referencing breaks.

See here:

Props to @lafriks for zeroing in the bug.