Ensure terminal size is sane if it is currently 0x0

[krader1961]

Long ago I fixed a zero day bug in the fish shell triggered if the termios rows and column values are both zero. Such as can happen if using a Linux serial console. If the size is 0x0 (rows by columns) assume the size is 24x80 (for historical reasons). When this is implemented we can remove these lines from the expect based unit tests:

# Terminal rows and columns may default to zero so ensure sane values.
send "stty rows 24 cols 80\r"
expect_prompt