detach_window: Segfault when detaching a single window on macOS

[rafikdraoui]

Kitty 0.15.0, macOS 10.14.6

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$ echo "map kitty_mod+d detach_window new-tab" > detach.conf
$ kitty -c detach.conf

Then entering the following keystrokes in sequence (create new window, detach to new tab, detach to new tab):

kitty_mod+enter
kitty_mod+d
kitty_mod+d

will result in:

'kitty -c detach.conf' terminated by signal SIGSEGV (Address boundary error)

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On Linux, kitty doesn't crash, but the above steps will often lead to colors getting messed up. I haven't found a minimal reproducible case for that yet, but I suspect that the cause is the same as for the segfault on macOS