MM-31062: Rewrite empty string checks to be more idiomatic (#16587)

https://mattermost.atlassian.net/browse/MM-31062

```release-note
NONE
```

app/user.go

@@ -1497,7 +1497,7 @@ func (a *App) SendPasswordReset(email string, siteURL string) (bool, *model.AppE
 		return false, nil
 	}
 
-	if user.AuthData != nil && len(*user.AuthData) != 0 {
+	if user.AuthData != nil && *user.AuthData != "" {
 		return false, model.NewAppError("SendPasswordReset", "api.user.send_password_reset.sso.app_error", nil, "userId="+user.Id, http.StatusBadRequest)
 	}