fix: guard against undefined commandShortcuts when saving shortcuts

[arashsheyda]

Description

Saving a keyboard shortcut would throw Cannot set properties of undefined when commandShortcuts was missing from persisted settings (e.g. settings saved before this field existed).

Linked Issues

closes #263

Additional context

[pkg-pr-new]

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@vitejs/devtools

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@vitejs/devtools-kit

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@vitejs/devtools-rolldown

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@vitejs/devtools-rpc

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@vitejs/devtools-self-inspect

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commit: 5784360

[antfu]

But with mergeInitialValue it should have always be initilized - so if there is something wrong on that, it's better for us to fix that instead, otherwise the similar issue could occur again when we add new values in the the settings

[arashsheyda]

oh I didn't realize. I try to put a fresh reproduction, thanks