feat: don't completely bail if support data does not exist

[pemrouz]

I'm currently working on dynamically transpiling resources with the minimum set of transformations required by that browser, and it would be useful to not bail if a version is specified for which there is no support data. Defaulting to either bitmask is fine (or perhaps by specifying a "fallback" option).

@Rich-Harris, I'm happy to open a PR just wanted to run this by you first. Let me know what you think..