Skip through and skipUpTo *sometimes* freeze the image when skipping in a block

[adri09070]

This is part of the problem described by #13.

Bug: Sometimes, when we skip in a block, the image freezes. This is not due to #26 as I got the issue when I tried to skip a single instruction inside a block.

How to reproduce the bug: If you debug:

DoIt

    | a b |
    b := 1.
    [ 
    a := 2.
    a := b := 3 + 2 ] value.
    ^ 42

and that you do: stepOver, stepOver and stepThrough to enter the block. If you skip through the assignment a:=2, this is skipped correctly. Then, if you skip up to the assignment b := 3 + 2, the image freezes.

Proof that the block is the problem: If you debug the block content outside of the block:

DoIt
    a := 2.
    a := b := 3 + 2

and if you skip the exact same instructions, the image doesn't freeze.

I have to investigate more why the image freezes when trying to skip certain instructions and not others, and why the block is problematic.