Fixes to SqlServer script logging

When script output logging is enabled on the SqlScriptExecutor, it blows
up on statements that don't return any rows (InvalidOperationException:
"sequence contains no elements" from the Max call). It also spews a lot
of noise on scalar statements (prints parts of the empty header table).
Fixed those issues. Also cleaned up the case where the header table is
malformed when a column name is longer than the row data in each column
(including when there's no row data).
Added null check before checking the length of the line.
Merge branch 'master' of github.com:nitzmahone/DbUp into nitzmahone-master
Merge branch 'nitzmahone-master'