If I understand this correctly it means that a test for the SVG table
is not sufficient. Instead, you have to actually do the call to
`driver->clazz->load_glyph`, and if this fails, FreeType should try to
load a bitmap font, and if this fails, it should proceed with
auto-hinting the glyph from the `glyf` table.
The load_glyph call won't fail even if an OT-SVG glyph is not found, I think. Instead, it'll resort to whatever type of glyph is found. That's the current behavior of cff_slot_load and TT_Load_Glyph.
If necessary, `tt_face_load_svg_doc` should be modified to exit
quickly if there is no SVG corresponding glyph.