Fix corpus tests substitute font spacing

CL changing behavior:
https://pdfium-review.googlesource.com/c/6630/

Bug: chromium:431507
Change-Id: I6f87de0a143379d674d357af70d0690dd8e7ee0b
Reviewed-on: https://pdfium-review.googlesource.com/6713
Reviewed-by: dsinclair <dsinclair@chromium.org>
5 files changed