fix(plugin-legacy): use terser when minifier is not specified

[OrekiSH]

Description

Only use terser as the default minifier when minifier is not specified, minify: false is useful in some cases I think.

Additional context

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What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[antfu]

Suggested change

	const { minify } = config.build
	if (typeof minify === 'undefined') {
	config.build.minify = 'terser'
	if (!config.build || config.build.minify === undefined) {
	return { build: { minify: 'terser' } }

I think we should use return instead of mutating the config object directly. (also the case that config.build might be undefinded.

[OrekiSH]

Well, in factconfig.build has been set to {} if not exists in line 86. And return value in config option is a little confusing for me. It seems like no param reassign, but it actually mutated config globally.🤔

[sapphi-red]

It seems this is covered with #6272.

[patak-cat]

Closing the PR as it covered as stated by @sapphi-red. @OrekiSH let us know if minify: false isn't working as expected for you. And thanks for the PR