Fix op_read_char to accept optional timing arguments

Lost Pig calls read_char with only the required first operand.
The Z-machine spec says time and input_routine are optional.

src/mudlib/zmachine/zcpu.py

@@ -906,7 +906,7 @@ class ZCpu:
         """Play sound effect (no-op - sound not supported in text MUD)."""
         pass
 
-    def op_read_char(self, unused, time, input_routine):
+    def op_read_char(self, unused, time=0, input_routine=0):
         """Read a single character from input stream 0 (keyboard).
 
         Optionally, call a routine periodically to decide whether or