Stepper: does not get stuck when it should. Instead it does not respond!

[martin-henz]

Example program:

1(2 * 3);

The stepper should produce the following steps:

1(2 * 3);
->
1(6);

Ideally, the last step should be indicated as "being stuck".

Another example:

1 + '2';

[martin-henz]

This issue is resolved in the current version, except #1622.