[REVIEW-3-5] fix for fdo#47503, crash opening a xls file with chart

[Markus Mohrhard]

Hey,

[1] fixes the crash opening the file in fdo#47503. The code in
ScDocument::HasData needs to check that the sheet index is valid
before it uses the sheet index to access the table.

This patch is simple and safe and I think we easily integrate it into 3-5.

Regards,
Markus

[1] http://cgit.freedesktop.org/libreoffice/core/commit/?id=95c65a363fa4cd0cbbfa93d53e10d86b3fb275f2