macos: Fix panic when `NSWindow::screen` returns `nil` (#38524)

Closes #ISSUE

Release Notes:

- mac: Fixed an issue where Zed would panic if the workspace window was
previously off screen
4e316c683bBen Kunkle committed on 9/19/2025, 7:07:02 PM· committed by GitHubparent1afbfcb
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