lib/model: Wait for folder to stop (fixes #4981) (#4982)

lib/model/model.go

@@ -344,10 +344,14 @@ func (m *Model) RemoveFolder(cfg config.FolderConfiguration) {
 }
 
 func (m *Model) tearDownFolderLocked(cfg config.FolderConfiguration) {
-	// Stop the services running for this folder
-	for _, id := range m.folderRunnerTokens[cfg.ID] {
-		m.Remove(id)
+	// Stop the services running for this folder and wait for them to finish
+	// stopping to prevent races on restart.
+	tokens := m.folderRunnerTokens[cfg.ID]
+	m.fmut.Unlock()
+	for _, id := range tokens {
+		m.RemoveAndWait(id, 0)
 	}
+	m.fmut.Lock()
 
 	// Close connections to affected devices
 	for _, dev := range cfg.Devices {