leaving device path field blank when creating new local storage-based SR shouldn't be allowed before clicking finish

[pricemc1]

Issue: When you go to create a new SR using the 'local storage' option it allows you to leave the device path field blank and click the finish button. If you do this it tries for a while to create something and finally throw a 'no such device ' error. Since there is no auto-discovery or default storage device it is trying to use, completion of the device path field should be mandatory before the program allows the finish button to be clicked.

Recreate:

XCP-ng: latest 8.3 release as of 11/12/2024
XCP-ng Center: latest release as of 11/12/2024

1. Right-click host and choose "New SR...'
2. In wizard, on Type page, select 'local storage' radio button and click Next.
3. On Name page click Next.
4. On Location page select 'ext' radio button and click Finish.