directory: fix update in root directory

Commit 0bfe7802 broke update for new files in the root directory,
because music_root->path was an empty string and not NULL.  There were
some NULL tests missing.  Change them to !isRootDirectory(path)
instead of path!=NULL.

src/dbUtils.c

@@ -61,7 +61,7 @@ static int
 printDirectoryInDirectory(struct directory *directory, void *data)
 {
 	struct client *client = data;
-	if (directory->path) {
+	if (!isRootDirectory(directory->path)) {
 		client_printf(client, "directory: %s\n", directory_get_path(directory));
 	}
 	return 0;
@@ -371,7 +371,7 @@ sumSavedFilenameMemoryInDirectory(struct directory *dir, void *data)
 {
 	int *sum = data;
 
-	if (!dir->path)
+	if (isRootDirectory(dir->path))
 		return 0;
 
 	*sum += (strlen(directory_get_path(dir)) + 1

src/song_print.c

@@ -26,7 +26,7 @@
 void
 song_print_url(struct client *client, struct song *song)
 {
-	if (song->parent && song->parent->path) {
+	if (song->parent && !isRootDirectory(song->parent->path)) {
 		client_printf(client, "%s%s/%s\n", SONG_FILE,
 			      directory_get_path(song->parent), song->url);
 	} else {

src/update.c

@@ -291,7 +291,7 @@ updateDirectory(struct directory *directory)
 		if (!utf8)
 			continue;
 
-		if (directory->path)
+		if (!isRootDirectory(directory->path))
 			utf8 = pfx_dir(path_max_tmp, utf8, strlen(utf8),
 			               dirname, strlen(dirname));
 		if (was_empty) {