src/libFLAC/stream_decoder.c : Fix seek bug.

Janne Hyvärinen reported a problem with seeking as a result of the
fix for CVE-2014-9028. This is a different solution to the issue
that should not adversely affect seeking.

This version of the fix for the above CVE has been extensively fuzz
tested using afl (http://lcamtuf.coredump.cx/afl/).

Reported-by: Janne Hyvärinen <cse@sci.fi>