nsb13: red border not completely deleted

[heppg]

worked with blocks having errors. Here scenario, and although text is long, the bug is minor.

operator divide by zero, operator goes red (ok). move by (divide by 0), operator red, block gets red border. the more blocks in the chain, the more blocks inside red border (ok). Having three blocks, with red border as seen here, I cut out the middle one. The result is The border is available in fragments.

Unfortunately, the legacy scratch is not perfect with handling these red borders either.Here the situation with two blocks in error, and here I dragged the last block away: the first one keeps red border, the second one not. Which violates my sense of logic.

Also weird is the 'save picture of scripts', in legacy scratch and in nsb13, the red border is not fully exported. This could be an enhancement request.

[timrowledge]

Interesting; I think it might even help with working out what happens in #39