Reverted changes to WebDavVolume#getMountPoint()

See: https://github.com/cryptomator/cryptomator/pull/1307#discussion_r472888268

main/commons/src/main/java/org/cryptomator/common/vaults/WebDavVolume.java

@@ -27,6 +27,7 @@ public class WebDavVolume implements Volume {
 	private WebDavServer server;
 	private WebDavServletController servlet;
 	private Mounter.Mount mount;
+	private Path mountPoint;
 
 	@Inject
 	public WebDavVolume(Provider<WebDavServer> serverProvider, VaultSettings vaultSettings, Settings settings) {
@@ -97,7 +98,7 @@ public class WebDavVolume implements Volume {
 
 	@Override
 	public Optional<Path> getMountPoint() {
-		return Optional.empty(); //TODO
+		return Optional.ofNullable(mountPoint); //TODO
 	}
 
 	@Override