Large query file closes on its own after cancelling job and switching tabs

[ellbosch]

ADS alerts me with Unable to open 'file.sql - elbosc...elbosc)': Cannot read property 'length' of null. after switching back to a query file tab following the cancellation of a run. A 1 MB script file was used to produce the bug.

Particularly concerning is that ADS will close the file even if it is not saved. There is seemingly no way to restore the file.

Repro steps:

1. Save a large (i.e. 1 MB) .sql file on a Windows desktop.
2. Open the file in ADS.
3. Click 'Run' after connecting to DB.
4. Once job starts to run, click 'Cancel'.
5. Switch or open to a new window.
6. Switch back to the original file--file will close.