Fixing the previous unresolved bug before I was going on vacation.

Fixing the previous unresolved bug before I was going on vacation.
When using the AliLevel3 tracking class and reading from a rootfile
with the patched AliTPC (ASV) version, one can only read 1 whole slice
at once (npatches=1). This because in AliLevel3 class only 1 instance
of the AliL3FileHandler is taking care of reading the data from all
patches, and therefore the AliL3FileHandler::fLastIndex method fails when
reading patch by patch. This problem did not show up in the AliL3Hough,
because there you have one AliL3FileHandler per patch.