Stop watcher when unmounting

src/collection/collection.cpp

@@ -63,6 +63,7 @@ SCollection::SCollection(Application *app, QObject *parent)
 }
 
 SCollection::~SCollection() {
+  watcher_->Stop();
   watcher_->deleteLater();
   watcher_thread_->exit();
   watcher_thread_->wait(5000 /* five seconds */);

src/collection/collectionwatcher.cpp

@@ -684,6 +684,8 @@ QString CollectionWatcher::PickBestImage(const QStringList &images) {
   QString biggest_path;
 
   for (const QString &path : filtered) {
+    if (stop_requested_) return QString();
+
     QImage image(path);
     if (image.isNull()) continue;
 

src/device/filesystemdevice.cpp

@@ -67,6 +67,7 @@ bool FilesystemDevice::Init() {
 }
 
 FilesystemDevice::~FilesystemDevice() {
+  watcher_->Stop();
   watcher_->deleteLater();
   watcher_thread_->exit();
   watcher_thread_->wait();