Rollup merge of #156588 - Jules-Bertholet:fix-panicky-mapwindows-clone, r=Mark-Simulacrum

Don't drop uninit memory when `MapWindows::clone` panics

Fixes https://github.com/rust-lang/rust/issues/156501, using the approach suggested in @bjorn3's comment https://github.com/rust-lang/rust/pull/156517#discussion_r3232903243