[cff] Integer overflow.

Reported as

  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=2109
  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=2110
  https://bugs.chromium.org/p/oss-fuzz/issues/detail?id=2122

* src/cff/cf2blues.c (cf2_blues_init): Use OVERFLOW_SUB_INT32.

* src/cff/cf2hints.c (cf2_hintmap_map): Synchronize if-else
branches.
3 files changed