ra: Fix parsing of svn link with multiple lines
Some svn links might contain multiple lines if a user added an end of line character in the first line.
When exporting a link, subversion will only consider the first line content to create a symbolic link so we need to apply the same processing or the link we create will differ from the exported one.
Related to #3695
Migrated from D6704 (view on Phabricator)