Forcibly set the current seek location of gz files that we are accessing

via dup(fileno());gzdopen() because stdio might have buffered data from
the underlying file meaning that the underlying seek position isn't what
we think it is.

libs/fst/fstapi.cc

@@ -4272,6 +4272,7 @@ int fstReaderInit(struct fstReaderContext *xc)
 #endif
 
         zfd = dup(fileno(xc->f));
+	lseek(zfd, ftell(xc->f), SEEK_SET);
         zhandle = gzdopen(zfd, "rb");
         if (zhandle) {
             for (offpnt = 0; offpnt < uclen; offpnt += FST_GZIO_LEN) {