Disable "Add" button on new processor dialog if no processors match search query

When adding a processor, if the search term does not match any available processors, the "Add" button should be disabled. If no processors are available, the user can still click the "Add" button and then receives an error message stating "The type of processor to create must be selected."

To reproduce:

1. Drag a new processor onto the canvas
2. Type "sdfsdf" into the search field
3. Click "Add"