GetChar1
Implements ISO's get_char/1: reads (consuming it) the next character from the current input stream (see IOPrimitiveUtils.currentInputChannel) and unifies it with the argument, as the end_of_file atom at end of stream.
Throws
(in_character) if the argument is bound to something other than end_of_file or a one-character atom.
Fails, rather than erroring, if the channel is closed.