Change deleteCell behavior when there are no cells

Change deleteCell behavior when there are no cells, according
to the spec [1] when the index is -1 and there are no cells
we should not do anything.

Behavior matches Firefox, Safari and Edge.

BUG=651762
[1] https://html.spec.whatwg.org/multipage/tables.html#dom-tr-deletecell

Review-Url: https://codereview.chromium.org/2406423004
Cr-Commit-Position: refs/heads/master@{#424869}
2 files changed