I/O [NT]: Reading from the console on NT may fail with ENOMEM.

Reading from the console on NT uses system buffers of limited size
(nominal limit 64K, in practice 26608 or 31004 bytes), and will
fail with ERROR_NOT_ENOUGH_MEMORY if an attempt is made to read
more data than the limit.

Fixes interactive Hilfe terminating with "Terminal closed." on start on NT.