[parrot/parrot] bd63ea: [pmc] rpa: fix a resize edgecase with size=0

[GitHub]

  Branch: refs/heads/smoke-me/rpa-offset-gh1152
  Home:   https://github.com/parrot/parrot
  Commit: bd63ea782e0d9111b42c44d3ed1eff601a0b0f59
      https://github.com/parrot/parrot/commit/bd63ea782e0d9111b42c44d3ed1eff601a0b0f59
  Author: Reini Urban <rurban at cpanel.net>
  Date:   2014-12-02 (Tue, 02 Dec 2014)

  Changed paths:
    M src/pmc/resizablepmcarray.pmc

  Log Message:
  -----------
  [pmc] rpa: fix a resize edgecase with size=0

avoid negative offsets.
repro:
  valgrind ./parrot_old -t20 parrot-nqp.pbc --target=pir compilers/data_json/JSON.nqp