[Installer] Destination field is empty in target support installers if Unity is not installed

Steps to reproduce:
0. Do not install Unity.
1. Run any of Target support installers (e.g. Android).
2. Navigate to Choose install location step.

Actual result: Destination folder is empty.
Expected result: If Unity is not installed, and we pre-check it, we should or not allow user to proceed to this step, or we should at least add some predefined path there (like C:\Program Files).