RFR(XS): 8137260: fix warning after "8046148: JEP 158: Unified JVM Logging"

[Lindenmaier, Goetz]

Hi,

we see warning
"negative integer implicitly converted to unsigned type"
for
size_t first_pos = -1;
with gcc 4.1.2.

I fixed this by using SIZE_MAX.

Please review this tiny change.  I please need a sponsor.
http://cr.openjdk.java.net/~goetz/webrevs/8137260-fixWarn/webrev.00/


Thanks and best regards,
  Goetz.