Glyph cache optimization

Precaching at startup was not working. One-liner fix to init the caches
so that precaching would kick in earlier, saving time at startup by avoiding
the multiple-upload issue of caching at render time.

Issue #6893691 long app launch time on manta for some apps comparing to nakasi/stingray

Change-Id: Ie5c7f0536ec8ea371c7892e5e09c1db14795531c