cleanup

src/main/java/org/cryptomator/ui/fxapp/AppLaunchEventHandler.java

@@ -72,7 +72,6 @@ class AppLaunchEventHandler {
 
 	// TODO deduplicate MainWindowController...
 	private void openPotentialVault(Path path) {
-		assert !Platform.isFxApplicationThread();
 		Path potentialVaultPath = path.getFileName().toString().endsWith(CRYPTOMATOR_FILENAME_EXT) ? path.getParent() : path;
 		Optional<Vault> existing = vaultListManager.get(potentialVaultPath.normalize().toAbsolutePath());
 		if (existing.isPresent()) {

src/main/java/org/cryptomator/ui/mainwindow/VaultListController.java

@@ -338,7 +338,8 @@ public class VaultListController implements FxController {
 				LOG.warn("Cannot add {}: {}", target, e.getMessage());
 				Platform.runLater(() -> dialogs.prepareNotAVaultDirectoryDialog(mainWindow, e).build().showAndWait());
 			} catch (IOException e) {
-				LOG.error("Failed to add vault {}", target, e);
+				LOG.warn("Failed to add vault {}", target, e);
+				Platform.runLater(() -> appWindows.showErrorWindow(e, mainWindow, null));
 			}
 		});
 	}