RFR(XXS): 8086073: Fix PrintStubCode for empty StubCodeGenerator.

[Lindenmaier, Goetz]

Hi,

PrintStubCode runs into an assertion if a StubCodeGenerator that never generated
a stub is deleted. This happens for ICacheStubGenerator on ppc, as we implement
the flushing with inline assembly and don't generate a stub.

The fix is to check for an empty list in the assertion.

Please review and sponsor this tiny fix.
http://cr.openjdk.java.net/~goetz/webrevs/8086073-PSC/webrev.01/


Best regards and thanks,
  Goetz.