Fix file descriptor and memory leaks in libdpv

[dteske]

Summary

Close /dev/tty in tty_maxsize_update() if we open it
in the !isatty(fd) case to avoid leaking the descriptor.
Verify that we were actually able to open /dev/tty.

Don't leak a file descriptor and a process in x11_maxsize_update()
if fgets() fails.

[dteske]

Take

[dteske]

I've only a couple changes I'll make before committing with reference to OP. Instead of "doclose" I will use "opened" which makes the code easier to read.

[truckman]

That sounds reasonable to me.

[dteske]

Sorry for the delay, had a disk failure take out my operations for a full 4 weeks, but finally got all the data recovered and back up and running