Bug#782831: libvorbis: use of non-initialized variable leads to SIGSEV in dhewm3

[Martin Steghöfer]

Update: This is related to the beginning-of-stream special case for 
seeking and to the fact that there is only one "normal" ogg page in the 
file. The first time this special case is used, it seems to advance the 
page pointer to a place where the same special case cannot find any page 
during the second seek because the stream ends (that type of seeking 
works only forward).