Fix some minor file descriptor leaks and related glitches.

Fix some minor file descriptor leaks and related glitches.

* filelock.c (create_lock_file) [!O_CLOEXEC]: Use fcntl with FD_CLOEXEC.
(create_lock_file): Use write, not emacs_write.
* image.c (slurp_file, png_load_body):
* process.c (Fnetwork_interface_list, Fnetwork_interface_info)
(server_accept_connection):
Don't leak an fd on memory allocation failure.
* image.c (slurp_file): Add a cheap heuristic for growing files.
* xfaces.c (Fx_load_color_file): Block input around the fopen too,
as that's what the other routines do.  Maybe input need not be
blocked at all, but it's better to be consistent.
Avoid undefined behavior when strlen is zero.