fix: setup preparser correctly when no addons are used

[oripka]

Currently the preparser is only called if addons.length > 0. If no addons are used the preparser does not work. This fixes that issue.

[netlify]

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[KermanX]

Thanks a lot~

[pkg-pr-new]

Open in Stackblitz

@slidev/client

pnpm add https://pkg.pr.new/slidevjs/slidev/@slidev/client@1951

@slidev/parser

pnpm add https://pkg.pr.new/slidevjs/slidev/@slidev/parser@1951

create-slidev

pnpm add https://pkg.pr.new/slidevjs/slidev/create-slidev@1951

@slidev/cli

pnpm add https://pkg.pr.new/slidevjs/slidev/@slidev/cli@1951

create-slidev-theme

pnpm add https://pkg.pr.new/slidevjs/slidev/create-slidev-theme@1951

@slidev/types

pnpm add https://pkg.pr.new/slidevjs/slidev/@slidev/types@1951

commit: c5a319d