fix(ps1): replace null-conditional operator for PowerShell 5.1 compatibility (#1975)

The `?.` (null-conditional member access) operator requires PowerShell 7.1+,
but Windows ships with PowerShell 5.1 by default. When AI agents invoke .ps1
scripts on Windows, they typically use the system-associated handler (5.1),
causing a ParseException: Unexpected token '?.Path'.

Replace the single `?.` usage with a 5.1-compatible two-step pattern that
preserves the same null-safety behavior.

Fixes #1972