unset XDG_HOME_CONFIG as gitea manages configuration locations (#33067)

unset XDG_CONFIG_HOME early to enable gitea to manage git configuration.
simple error checking to satisfy the linting. Closes #33039

---------

Co-authored-by: wxiaoguang <wxiaoguang@gmail.com>

cmd/main.go

@@ -165,6 +165,7 @@ func NewMainApp(appVer AppVersion) *cli.App {
 	app.Commands = append(app.Commands, subCmdWithConfig...)
 	app.Commands = append(app.Commands, subCmdStandalone...)
 
+	setting.InitGiteaEnvVars()
 	return app
 }