[BUG] zle_highlight fails to highlight suffix added with compadd -R

[Marlon Richert <marlon.richert@xxxxxxxxx>]

The following completion functions give different highlighting results
in the zle:

_tst() { compadd -S '<SUFFIX>' -q -- '' }
_tst() { compadd -S '<SUFFIX>' -r '' -- '' }
_tst() { compadd -S '<SUFFIX>' -R '' -- '' }

With the first two functions, <SUFFIX> correctly gets highlighted as
autoremovable. However, with the third function, <SUFFIX> does not get
highlighted, even though it is autoremovable.