Zoomify - Fix for Wrong dimensions for marginal tiles for resolutions with dimensions dividable by tile size

- Fix for problem from this issue: https://github.com/openlayers/openlayers/issues/928
Added curly braces to meet coding style, corrected height variable instead of width on L242
Merge pull request #976 from michalbecak/master

Pull request for fix of this issue https://github.com/openlayers/openlayers/issues/928