CTS test for robust handling of invalid cmap

A large nGroups value in a format 12 cmap table in an OpenType font
can cause integer overflow. In that case, the font should be rejected
and its Unicode coverage not included in the fallback chain. This test
verifies that such invalid fonts are robustly rejected.

Bug: 25645298
Change-Id: Ifbab3aa352074a05a5615de05c2f8f35fe2dc595
3 files changed