* sysdeps/posix/posix_fallocate.c (posix_fallocate): If len == 0,

	* sysdeps/posix/posix_fallocate.c (posix_fallocate): If len == 0,
	call ftruncate if offset is bigger than current size.  Make sure
	the file is offset + len bytes long if that is more than current size.
	Don't overwrite previous content of the file.
	* sysdeps/posix/posix_fallocate64.c (__posix_fallocate64_l64):
	Likewise.