Fix locking (#1141)

* Fix unprotected section

* Optimize lock where only reads are performed

internal/photoprism/files.go

@@ -52,13 +52,12 @@ func (m *Files) Init() error {
 
 // Done should be called after all files have been processed.
 func (m *Files) Done() {
+	m.mutex.Lock()
+	defer m.mutex.Unlock()
 	if (len(m.files) - m.count) == 0 {
 		return
 	}
 
-	m.mutex.Lock()
-	defer m.mutex.Unlock()
-
 	m.count = 0
 	m.files = make(query.FileMap)
 }

internal/photoprism/photos.go

@@ -61,8 +61,8 @@ func (m *Photos) Remove(takenAt time.Time, cellId string) {
 func (m *Photos) Find(takenAt time.Time, cellId string) uint {
 	key := entity.MapKey(takenAt, cellId)
 
-	m.mutex.Lock()
-	defer m.mutex.Unlock()
+	m.mutex.RLock()
+	defer m.mutex.RUnlock()
 
 	return m.photos[key]
 }