Fix var() parsing in font-variation-settings
Similar to crrev.com/c/5554250, Peek() first to check for a block before
calling Consume().
Fixed: 342078742
Change-Id: Ibcc31c60b4e1d23b9942d1ccf8da689b413f974b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5560398
Reviewed-by: Steinar H Gunderson sesse@chromium.org
Commit-Queue: Kevin Babbitt kbabbitt@microsoft.com
Cr-Commit-Position: refs/heads/main@{#1305140}