lang: compile: Fix error handling on invalid command

lang/compile.py

@@ -190,7 +190,7 @@ def parse_command(line):
 		command = parse_set(line)
 	elif instr == "Return":
 		command = parse_return(line)
-	else:
+	if not command:
 		print("not a command? line: %s" % (' '.join(line)))
 		return None
 	return ASTCommand(command)