Fix an issue causing errors about bad return types

[daniell]

When trying to read an xlsx file, a java.lang.VerifyError is thrown saying that com.monitorjbl.clsc.impl.StreamingSheet.getPaneInformation expects to have a return type of org.apache.poi.hssf.util.PaneInformation but is getting org.apache.poi.ss.util.PaneInformation. This change should fix the issue.

[monitorjbl]

Nice catch! Would you mind including a test case with a sheet that has this condition? I don't doubt your change, but there's a lot of different sheets out in the wild. It'd be nice to include one for this case.

[daniell]

I'm having problems reproducing the issue in a test environment. It happens consistently when trying to upload a spreadsheet to a web app running on Tomcat 8, but I can't seem to get it to happen at all in tests. Not sure what to do about that.

[monitorjbl]

Alright, I'll go ahead and merge it anyway. The change appears to correct an incorrect usage of the hssf package, which is for the old XLS format. That's definitely incorrect for this library as it only supports XLSX (in the xssf package). The ss package is supposed to be the format-agnostic one.