Fix SkOrderedFontMgr::onMatchFamily

[samizdatco]

SkOrderedFontMgr's matchFamily currently has a bug where it will only look in the first FontMgr in its list when searching for fonts. The problem is that its search loop is expecting a null response to signal "no matches", but the actual behavior of FontMgr is to never return null. Instead it will return a zero-length SkFontStyleSet.

This PR adds a count() > 0 check to the return value rather than just checking whether it is non-null.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

View this failed invocation of the CLA check for more information.

For the most up to date status, view the checks section at the bottom of the pull request.

[skia-codereview-bot]

This PR (HEAD: 50f05e8) has been imported to Gerrit for code review.

Please visit review.skia.org/926716 to see it. Please CC yourself to the Gerrit change.

Note:

• Skia uses only Gerrit for reviews and submitting code (doc).
• All comments are handled within Gerrit. Any comments on the GitHub PR will be ignored.
• The PR author can continue to upload commits to the branch used by the PR in order to address feedback from Gerrit.
• Once the code is ready to be merged, a maintainer will submit the change on Gerrit and skia-codereview-bot will close this PR.
• Similarly, if a change is abandoned on Gerrit, the corresponding PR will be closed with a note.