Avoid null pointer dereference in ct_font_descriptor_get_traits.
CFDictionaryGetValue can return NULL and CFNumberGetValue doesn't null-check.
Reported in https://bugs.gnucash.org/show_bug.cgi?id=799473.
CFDictionaryGetValue can return NULL and CFNumberGetValue doesn't null-check.
Reported in https://bugs.gnucash.org/show_bug.cgi?id=799473.