linux: don't abort on malformed /proc/stat
linux: don't abort on malformed /proc/stat

Return an error instead of aborting when /proc/stat doesn't have the
expected format.

PR-URL: https://github.com/libuv/libuv/pull/822
Reviewed-By: Colin Ihrig <838f779c91673db29b8572ea3f54d191d3878ae2@gmail.com>

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