fix: correctly close all file pointers when creating apple pty

[Patrick-Beuks]

This PR cleans up all file descriptors correctly as the before low_fds[0] could never be closed due to the count > 0 condition.

This makes it so that if the slave exits all tty descriptors can be cleaned.

Before this change the tty descriptors would keep increasing until the sysctl kern.tty.ptmx_max limit and closing terminals would not make possible to create new terminals.

This also fixes a logic error in that res = grantpt(*master) || unlockpt(*master); could never be -1

Note:
While this solves the issue with tty descriptors on successful creation, it can still leak descriptors when it fails before errors got to the done label. I tried adding a cleanup step on errors, but could not get it working in the time allotted to fix this problem.

[deepak1556]

Thank you for the PR, closing in favor of #882