./data/avatars used as avatar file of first organization created upon installing from scratch

[pmattern]

• Gitea version (or commit ref): d76d67d
• Git version: 2.12.0
• Operating system: Arch Linux x86_64
• Database (use [x]):
  • PostgreSQL 9.6.1
  • MySQL
  • SQLite
• Can you reproduce the bug at https://try.gitea.io:
  • Yes (provide example URL)
  • No
  • Not relevant

Description

When the first organization is created after installing from scratch, it is assigned a random icon which is saved as file ./data/avatars. This completely compromises any use of ./data/avatars as folder as usual.

To reproduce install Gitea from scratch, that is new database and so on, create an administrative user, have that user create the first organization of the Gitea instance and check the FHS.

The problem can not be seen when a directory ./data/avatars is created after installing but before creating the first organization or when an instance which preexists including a directory ./data/avatars is upgraded.
Either way new organizations are assigned the Gitea cup of tea as an icon, no longer the random icon as in earlier versions. I guess this is on purpose, but it is in contrast to a random icon still involved when the problem is manifest.
Permission issues weren't involved here as e. g. ./data/sessions is created as a folder and handled as usual.
Problem is a regression which didn't exist in 1f7837d which happens to be the last version I had installed from scratch.

EDIT Add behaviour when ./data/avatars preexists as directory plus some minor details.

[pmattern]

The problem is fixed running 2215840 under the very same circumstances as depicted in the initial comment here.