Orgs: fix org page title when full name is not defined

[silverwind]

This falls back to a organization's name when the full name is not defined, so the page title at https://try.gitea.io/my-cool-organization will become

my-cool-organization - Gitea: Git with a cup of tea

instead of the current

Gitea: Git with a cup of tea

The same functionality is already in place for user profile pages.

[strk]

LGTM

[lunny]

LGTM