Bugfix for losing autoFilter with multiple sheets

[heew]

Fixes issue #190

[lion2486]

The fix looks at first sign to be a reasonable one. Maybe the count($this->sheets) will get the same number but it's a quick fix.
Tested on my own and it works.

[hnx8]

I noticed when I was doing enhancement, as far as seeing the contents of the actual Xlsx file,
it seems more appropriate that the "localSheetId" are numbered in order from the first sheet, regardless of whether AutoFilter is specified or not.
(so, in # 207 I fixed it in a form that seemed better)