Git clone via SSH hangs when markup.asciidoc is partially defined in config

[dllud]

• Gitea version (or commit ref): 1.7.0
• Git version: 2.11.0
• Operating system: Debian 9 (stable)
• Database (use [x]):
  • PostgreSQL
  • MySQL
  • MSSQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant
• Log gist:

Description

Adding the markup.asciidoc section to the app.ini config file without having all properties defined causes git clone via ssh to hang.
I bumped into this issue after adding the markup.asciidoc section to my old config file, but I was able to reproduce the issue on a new installation with a config file generated from scratch by gitea 1.7.0.

Adding the section, with all properties defined, causes no problem (example bellow):

[markup.asciidoc]
ENABLED = false
; List of file extensions that should be rendered by an external command
FILE_EXTENSIONS = .adoc,.asciidoc
; External command to render all matching extensions
RENDER_COMMAND = "asciidoc --out-file=- -"
; Don't pass the file on STDIN, pass the filename as argument instead.
IS_INPUT_FILE = false

Commenting or deleting just one property causes the hang:

[markup.asciidoc]
ENABLED = false
; List of file extensions that should be rendered by an external command
;FILE_EXTENSIONS = .adoc,.asciidoc
; External command to render all matching extensions
RENDER_COMMAND = "asciidoc --out-file=- -"
; Don't pass the file on STDIN, pass the filename as argument instead.
IS_INPUT_FILE = false

Even adding just the section header causes ssh git clone to hang:

[markup.asciidoc]

This issue seems related to #5386.

[zeripath]

The problem is caused by any log.Warn in func NewContext() in setting.go.

The issue is that these are outputted on stdout which confuses git.