symbol-cli.config.json - manual deletion causes failure

[davehodgson]

1. Expected: If I delete the contents of the file (or file itself) that CLI can recover and recreate it. Actual: If you empty the file, it can't add any new profiles nor can it list them

2. Open symbol-cli.config.json delete contents, save, go to terminal and run symbol-cli profile list

3. Ubuntu 20.04

It relies on the file having {} in it, if its empty it can't cope.

The inability to delete profiles in the CLI means this is the only obvious way to remove them, putting {} back into the file fixes it, we just need the parser/test to interpret empty file as {} or put {} back into the file if its empty and re-open