[io] Fix GC-related bug in Parrot_io_read_buffer
[io] Fix GC-related bug in Parrot_io_read_buffer

If Parrot_str_new_init triggers a GC run, out_buf might become invalid.

git-svn-id: 6e74a02f85675cec270f5d931b0f6998666294a3@49298 d31e2699-5ff4-0310-a27c-f18f2fbe73fe

gitster/parrot,youprofit/parrot,fernandobrito/parrot,gitster/parrot,tewk/parrot-select,gitster/parrot,parrot/parrot,FROGGS/parrot,fernandobrito/parrot,youprofit/parrot,tewk/parrot-select,gagern/parrot,tewk/parrot-select,gagern/parrot,tewk/parrot-select,FROGGS/parrot,gitster/parrot,parrot/parrot,youprofit/parrot,FROGGS/parrot,tkob/parrot,tkob/parrot,youprofit/parrot,tewk/parrot-select,tewk/parrot-select,gagern/parrot,FROGGS/parrot,tkob/parrot,gagern/parrot,gagern/parrot,gitster/parrot,fernandobrito/parrot,FROGGS/parrot,fernandobrito/parrot,parrot/parrot,tkob/parrot,gagern/parrot,FROGGS/parrot,parrot/parrot,tkob/parrot,fernandobrito/parrot,gagern/parrot,tkob/parrot,tkob/parrot,youprofit/parrot,gitster/parrot,FROGGS/parrot,FROGGS/parrot,fernandobrito/parrot,youprofit/parrot,gitster/parrot,tewk/parrot-select,parrot/parrot,fernandobrito/parrot,youprofit/parrot,youprofit/parrot,tkob/parrot