if --no-dedup was enabled in a volume which already contained
symlinked duplicate files, renaming/moving folders could fail
this is due to folder contents being moved one file at a time
(which is how symlink breakage is prevented) except the links
are moved assuming the final directory layout, meaning they
may be intermittently broken during the movie
with no-dedup, the symlinks are converted into full files as
each symlink is encountered, but a temporarily broken symlink
would crash the procedure
fix this by giving `_symlink` a new parameter `fsrc`
which is a known valid inode for data copying purposes
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