sys/base/readlink: bugfix for 'readlink -m'
sys/base/readlink: bugfix for 'readlink -m'

When 'readlink -m' (canonicalise nonexisting path) encountered a
symlink pointing to a nonexistent or non-directory target, it would
canonicalise up to that symlink and then fail to process the
remaining (nonexistent by definition) pathname elements.

The fix is, instead of returning after the recursive
_Msh_doReadLink_canon() call, to set the loop variable to its
result and continue.

modernish/modernish