Small fix to diagnostic-underlines when def:warning or def:error is missing from style.
Small fix to diagnostic-underlines when def:warning or def:error is missing from style.

eidheim/jucipp,cppit/jucipp,cppit/jucipp,cppit/jucipp,zalox/jucipp,eidheim/jucipp,zalox/jucipp,zalox/jucipp,eidheim/jucipp