fix FM svg harness

Without this we'd assert on empty container size.

Change-Id: I697d607af40ac6e62039be33aedb8ff1732d41b8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/364839
Reviewed-by: Mike Klein <mtklein@google.com>
Commit-Queue: Mike Klein <mtklein@google.com>
1 file changed