Fix GH-16523: FILTER_FLAG_HOSTNAME accepts ending hyphen

Domain name labels must not end with a hyphen, and that is also true
for the last label. Apparently, this has been overlooked so

Fix GH-16523: FILTER_FLAG_HOSTNAME accepts ending hyphen

Domain name labels must not end with a hyphen, and that is also true
for the last label. Apparently, this has been overlooked so far.

Closes GH-16540.

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