Regression fix.

- Properly fix `company-preview-frontend', amend last two commits.

- When tooltip spans text with multi-line `display' property and
  e-o-b, insufficient newlines may be padded.

- Calling `recenter' with tooltip open may cause tooltip update to
  fail.

* company.el:

(company-pseudo-tooltip-show): Use overlay to disable `display'
property for region from (point) to (point-max) prior to padding
new lines, then adjust overlay to proper size. Do not maintain
`company-row', as certain commands (e.g. `recenter') may change
screen row number without triggering tooltip redraw. This
information can be inferred from the first element of
`company-line-overlays'.

(company-pseudo-tooltip-edit): Remove reference to `company-row',
use `overlay-start' and `vertical-motion' to setup call to
`company--create-line-overlay'. `(vertical-motion 0)' is safe here
because we are inside the outer overlay which disabled the
`display' property of the region.

(company-preview-show-at-point): Check for `(eobp)' and handle
accordingly.

* company-tests.el(company-preview-show-with-annotations): Update
  to reflect change.