Empty cells within cell range are not exported

[tealeg]

If you have an XLSX file that contains a row where not every column contains a value, then the blank fields are completely ommitted from the API. This is problematic because it makes it seem like all values are left packed. The most typical use case is actually that you want to export the structure with this fields intact (treating and Excel worksheet as a table).

Using the program xlsx2csv as an example we can see some input that should result in output like this:

A, B, C, D
1, , 3, 4

Actually appears as:

A, B, C, D
1,3,4

[tealeg]

This is caused by the XLSX format not outputting XML for these cells. We needed to read the range defined in the row (a string that looks like this "1:3", for example) and then check that each row contains the right cells. Where cells were missing we add them in as empty cells. I suspect there are still issues around this (particularly where the range doesn't start at 1), but for now I am happy to close this bug down.