Fix memory corruption. This took far too long to debug. Bah.
Fix memory corruption. This took far too long to debug. Bah.

svn path=/trunk/libcss/; revision=5628

prepare/netsurf_libcss,servo/libcss,zhuyadong/libcss,servo/libcss,zhuyadong/libcss,prepare/netsurf_libcss,zhuyadong/libcss,servo/libcss,prepare/netsurf_libcss