Behavior if both webkitdirectory and accept attributes are specified

[inexorabletash]

See https://bugs.chromium.org/p/chromium/issues/detail?id=102984

The expectation of at least one developer is that in this case:

<input type=file webkitdirectory accept="image/*">

... then if a directory is chosen, only image files would be included.

In Chrome, the accept attribute is ignored (similar to the multiple case in #24)

We should verify behavior in Firefox/Safari/Edge

[inexorabletash]

Firefox seems to ignore accept here as well.