In non-interactive mode, stop after first syntax error

Don't keep going in this case; let the user fix the first error.

Signed-off-by: Keith Packard <keithp@keithp.com>

snek-parse.c

@@ -195,6 +195,8 @@ snek_parse(void)
 		case parse_return_syntax:
 		default:
 			snek_error_syntax(snek_lex_text);
+			if (!snek_interactive)
+				return snek_parse_error;
 			{
 				/* Skip input until we get back to
 				 * zero indent