GetChar2
Implements ISO's get_char/2: reads (consuming it) the next character from the input stream identified by the first argument (an alias or $stream(...) term) and unifies it with the second, as end_of_file at end of stream.
Throws
if the first argument is unbound.
if it does not identify an open channel.
(stream_type) if it identifies an output channel instead.
(in_character) if the second argument is bound to something other than end_of_file or a one-character atom.
Fails, rather than erroring, if the channel is closed.