WhiteboxWorkflows: kernel dies if file not found

[CarlosGrohmann]

Hi John

Running WbW on Linux here. I noticed here that WbW has some issues when opening a file but it can't find it (like if you give the wrong name). When that happens, the kernel dies, and sometimes it will work again but sometimes it will keep dying for no reason (like when setting up the wb environment). I had a notebook in which the kernel was constantly dying (in the browser or in VScode), and then after a few days it started working again... really odd, and I can't pinpoint what changed. In any case, I suggest to include a check to see if the file exists, and return an error if not, but not just die...
cheers