fdm: close fd even if we didn't find it in our list

This behavior is debatable, but helps in error handling where we're
removing a bunch of descriptors where not all of them have been added
to the FDM yet.

fdm.c

@@ -130,6 +130,7 @@ fdm_del_internal(struct fdm *fdm, int fd, bool close_fd)
     }
 
     LOG_ERR("no such FD: %d", fd);
+    close(fd);
     return false;
 }