[BUG] org-colview: error from face list

[JV]

The recently added function `org-columns--line-face' calls 
`face-attribute' on the value of its local ref-face. If ref-face holds a 
face list rather than a single face, this causes an "Invalid face" error.

Since only the ref-face :foreground is used, perhaps this could just 
call `foreground-color-at-point'?

-Jeff