func (m *botMedia) cacheFile() string {
	if m.cfile == "" {
		return mediaDBCache
	}
	return m.cfile
}
cacheFile returns the name specified in cfile or a default name
if cfile is nil.
package main
import (
	"errors"
	"github.com/go-telegram-bot-api/telegram-bot-api"
	"log"
	"sync"
)
const (
	mediaDBCache = "media.json"
)
type botMedia struct {
	sync.RWMutex
	URLToMediaID map[string]string `json:"media"`
	cfile        string
}
func newBotMedia() *botMedia {
	return &botMedia{
		URLToMediaID: map[string]string{},
	}
}