Expand handling of empty glyphs to SDF and Path cases

Hoist the remaining empty checks into the common code.

Change-Id: Ib34cf8d1121aae62735566cc230cdc4429dfda19
Reviewed-on: https://skia-review.googlesource.com/c/173641
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Mike Klein <mtklein@google.com>
2 files changed