Add missing isatty(...) function (#790)

Depending on the use of ComfyUI this missing function can be called in certain code paths, such as used in yachalk

prestartup_script.py

@@ -214,6 +214,9 @@ try:
                 # Handle error
                 raise ValueError("The object does not have a fileno method")
 
+        def isatty(self):
+            return False
+
         def write(self, message):
             global is_start_mode