Fix for a lot of 'globals' data

### Bug description

When sending a lot of data (16KB?, 64KB? not sure) as globals the sandboxed script will fail, because it did not receive all of the data and tried to run the script on the incomplete data.

### Submitted bug fix
We use a separator character '\u0000' when sending the data to the sandbox to ensure that all data was received. So we accumulate all chunks until the separator is found and then execute the script with all data.