RFR(XS): 8098815: Assertion failure in CDS shared string archive support on Windows

[Tom Benson]

Hi,
Please review this change for JDK-8098815.  The CDS code which maps the 
shared strings from an archive file must check for a zero length before 
calling the G1 fill_archive_regions routine.  It already checks this 
before the earlier calls to check_archive_address and 
alloc_archive_regions, for which fill_archive_regions is the final step. 
The problem occurred only on Windows because the string table is not 
included in the archive there.

JBS:   https://bugs.openjdk.java.net/browse/JDK-8098815
Webrev: http://cr.openjdk.java.net/~tbenson/8098815/webrev.00/
Tested: JPRT

Thanks,
Tom