Move tests on the highlight path until after the blacklist is checked so
that blacklisted paths are not tested. This should prevent hangs on dead
remote filesystems provided the path is blacklisted in
X_ZSH_HIGHLIGHT_DIRS_BLACKLIST.
Updated tests to 'default' highlight as the blacklist is now checked
before the path is tested.
Bug: https://github.com/zsh-users/zsh-syntax-highlighting/issues/528