Fix PHP 8.1 "rawurlencode(null)" exception which blocks rendering a project page

After PHP 8.1 the function `rawurlencode()` does not accept anymore the `null` value.

Thus return an empty string when the input parameter is null instead of passing the input parameter to `rawurlencode()`.

Closes T15263

Test Plan:
Applied this change on top of D25144, D25145, D25146, D25147, D25151,
D25152, D25153 and D25163 and already existing Workboard located at
`/project/view/1/` finally rendered in web…
Repository: rARC Arcanist
Author: aklapper
Commit Date: May 4 2023