When a SegmentTermPositions object is reset via seek() it does not move
the proxStream to the correct position in case the term is the first one
in the dictionary.
The reason for this behavior is that the skipStream is only moved if
lazySkipPointer is != 0. But 0 is a valid value for the posting list of
the very first term. The fix is easy: We simply have to set lazySkipPointer
to -1 in case no lazy skip has to be performed and then we only move the
skipStream if lazySkipPointer!=-1.