Although, the empty text should've been removed, but it may happen without the
normalization. Therefore, the lambda should keep scanning the first visible
char with ignoring empty `Text` nodes.
Additionally, there are similar methods which have the same lambda. Therefore,
this fixes them too.
I think we should make the scanner method take an option parameter to ignore
empty `Text` in a follow up bug.
Differential Revision: https://phabricator.services.mozilla.com/D242264
9253bce1c4