static/frontend/vuln: update copy for affected versions
static/frontend/vuln: update copy for affected versions

If "Affected Versions" is empty (which means both fixed and found
are empty) we  label that as "all versions, no known fixed", since
all versions are affected.

Change-Id: I29e1a4cb9b2085a0e2cf6b5b7ce1d07ed747ca30
Reviewed-on: https://go-review.googlesource.com/c/pkgsite/+/427539
TryBot-Result: kokoro <2ac7b1f3fa578934c95181d4272be0d3bca00121@google.com>
Reviewed-by: Julie Qiu <e6cb64861edcc38971590ff27c111e0e672de045@google.com>
Auto-Submit: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>
Run-TryBot: Jamal Carvalho <e0195770807aa8c82b0b128d9c0423b5ad035172@golang.org>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite