OSV-2021-389 Bad-cast to tt_cmap_t' (aka 'struct _tt_cmap')_cairo_truetype_index_to_ucs4

OSS-Fuzz report: https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=30823 Crash type: Bad-cast Crash state: Bad-cast to ttcmapt' aka 'struct ttcmap'cairotruetypeindextoucs4 cairosubfontglyphlookupunicode cairosubfontmapglyph...