rofiles-fuse: Handle operations on the root

ENSURE_RELPATH breaks when path is "/". In that case we need
to return "." instead of "".

https://bugzilla.gnome.org/show_bug.cgi?id=762596

src/rofiles-fuse/main.c

@@ -46,7 +46,10 @@ static GHashTable *created_devino_hash = NULL;
 static inline const char *
 ENSURE_RELPATH (const char *path)
 {
-  return path + strspn (path, "/");
+  path = path + strspn (path, "/");
+  if (*path == 0)
+    return ".";
+  return path;
 }
 
 typedef struct {