White space is not preserved when link-reference text is split over lines

[egnha]

As of a8ed64b,

roc_proc_text(rd_roclet(), "
  #' Title
  #' 
  #' Some [link text
  #' split over lines][pkg::fun()].
  #'
  #' @md
  foo <- function() {}")[[1]]

collapses the white space between the words “text” and “split”:

% Generated by roxygen2: do not edit by hand
% Please edit documentation in RtmpBGoS8c/file16a1a34b1d2a0
\name{foo}
\alias{foo}
\title{Title}
\usage{
foo()
}
\description{
Some \link[pkg:fun]{link textsplit over lines}.
}

The cause is the same as in #628 (which was fixed in #630).