[Bug 21722] Fix boolean logic on when to show placeholder text

Fixes Bug: https://www.w3.org/Bugs/Public/show_bug.cgi?id=21722

This aligns one section of the spec with the same [corrected] logic in
another part of the spec: the placeholder text should NOT show when just
the element is not focused...

(cherry picked from commit 41a12ca1a185370c17a0b5f3f3376e6f1e5b5a83)