D21467: fix highlighting of '\0' in C mode

[Christoph Cullmann]

cullmann added reviewers: dhaumann, vkrause, nibags.

REPOSITORY
  R216 Syntax Highlighting

REVISION DETAIL
  https://phabricator.kde.org/D21467

To: cullmann, dhaumann, vkrause, nibags
Cc: kwrite-devel, kde-frameworks-devel, domson, michaelh, ngraham, bruns, 
demsking, cullmann, sars, dhaumann