More robust team exists api endpoint (#12130)

* More robust team exists api endpoint

* Making the code more concise

* Better handling of errors on GetTeamByName

app/team.go

@@ -643,12 +643,7 @@ func (a *App) GetTeam(teamId string) (*model.Team, *model.AppError) {
 }
 
 func (a *App) GetTeamByName(name string) (*model.Team, *model.AppError) {
-	team, err := a.Srv.Store.Team().GetByName(name)
-	if err != nil {
-		err.StatusCode = http.StatusNotFound
-		return nil, err
-	}
-	return team, nil
+	return a.Srv.Store.Team().GetByName(name)
 }
 
 func (a *App) GetTeamByInviteId(inviteId string) (*model.Team, *model.AppError) {