Use FcConfigReference/Destroy appropriately instead of FcConfigGetCurrent

This may improves to be MT-safe.

Reported at https://bugs.chromium.org/p/chromium/issues/detail?id=1004254
3 jobs for mt-safe in 8 minutes and 44 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Build
passed mingw-build #863410

00:08:44

passed shared-build #863408

00:05:31

passed static-build #863409

00:04:27