fix(shared): add optional chain to `isInElectron` env

[danielj247]

Description

I have set-up a laravel, inertia and vue project and integrated devtools-next but kept getting errors on running vite:

failed to load config from {project dir}/vite.config.js
error when starting dev server:
TypeError: Cannot read properties of undefined (reading 'toLowerCase')

Solution

The first conditional in isInElectron checks if the navigator class exists, it does but it is empty - so the userAgent is undefined. I've added an optional chain to the end of the userAgent to ensure it's existence.

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