Handle vendor IDs that are fewer than 4 characters

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Description

The OS/2 Vendor ID is specced as a string of four characters. However, a font Vendor ID will often be fewer than four characters, so this field gets filled in with either spaces or null characters. For example, here’s how vendor ABC might appear:

<achVendID value="ABC\x00"/>

<achVendID value="ABC "/>

So, this PR strips those filled characters out before comparing the vendor ID against the configured expectation.

Checklist

• [x] update CHANGELOG.md
• [ ] wait for the tests to pass
• [ ] request a review

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Apparently, this was actually an issue in FontMake that was fixed already. So, this PR is irrelevant.