Generate Table Cell if Row Doesn't Have Any

[oleibman]

Description

Fix #2505. Word treats file as corrupt if a table row does not contain a cell (documentation for why this is so is included in the issue). Person reporting the issue suggests that dropping such a row from the output file is preferred. However, I think generating an empty cell instead is closer to the user's expectation. For example, as demonstrated in the unit tests added with this PR, if a table has row 1 and 3 which contain cells, but row 2 does not, the table as written to the file will have 3 rows, with the second containing an empty cell.

Checklist:

• I have run composer run-script check --timeout=0 and no errors were reported
• The new code is covered by unit tests (check build/coverage for coverage report)
• I have updated the documentation to describe the changes

[coveralls]

coverage: 97.209% (+0.001%) from 97.208%
when pulling 054d0d0 on oleibman:word2505b
into 2daa50c on PHPOffice:master.

[lucasnetau]

Hi @oleibman , tested locally and LGTM. Thank you.

[Progi1984]

@oleibman Great job.

Added some comments.
Could you update the changelog file, too, please ?

[oleibman]

@Progi1984 Change log updated, all your suggestions except one are incorporated; that one needs further discussion,