aux/primconvert: handle singular incomplete restarts
if no restart indices are found, this draw must be discarded to avoid crashing later on
Fixes: 58307074 ("util/primconvert: handle rewriting of prim-restart draws with unsupported primtype")
if no restart indices are found, this draw must be discarded to avoid crashing later on
Fixes: 58307074 ("util/primconvert: handle rewriting of prim-restart draws with unsupported primtype")