graphics/copperspice: unbreak with clang 4.0

../3rdparty/webkit/Source/WebCore/html/HTMLImageElement.cpp:77:24: error: ordered comparison between pointer and zero ('const int *' and 'int')

if (optionalHeight > 0)
    ~~~~~~~~~~~~~~ ^ ~

PR: 216015
Reported by: antoine (via exp-run)
Obtained from: upstream (excerpt)