add option doesn't quote shawl executable path if started from path containing whitespace

[Bill-Stewart]

Reproduce:

1. Create subdirectory with name containing spaces
2. Copy shawl.exe to this subdirectory

3. From this subdirectory, run command:

   shawl add --name test -- "C:\Program Files\Test App\testapp.exe"

Expected service command line:

   "C:\Path with Spaces\shawl.exe" run --name test -- "C:\Program Files\Test App\testapp.exe"

Actual service command line:

   C:\Path with Spaces\shawl.exe run --name test -- "C:\Program Files\Test App\testapp.exe"

If this service startup command line works (presuming testapp.exe exists in that path), then the Windows command-line parsing magic is working, but for sure security scanners will flag this as an "unquoted service path" vulnerability; e.g.: https://www.tenable.com/plugins/nessus/63155

The recommendation is to quote the executable path, thus preventing any potential exploit.

[mtkennerly]

Thanks for reporting this! I'll fix this up.