hugolib: Avoid server panic on TOML mistake in i18n
hugolib: Avoid server panic on TOML mistake in i18n

Fixes #4942

gohugoio/hugo,fedelibre/hugo,anthonyfok/hugo,mdhender/hugo,gohugoio/hugo,fedelibre/hugo,gohugoio/hugo,mdhender/hugo,mdhender/hugo,fedelibre/hugo,anthonyfok/hugo,mdhender/hugo,anthonyfok/hugo,fedelibre/hugo