Fix deferred group initialization in membuffer cache.
Fix deferred group initialization in membuffer cache.

* subversion/libsvn_subr/cache-membuffer.c
  (initialize_group): Remove premature optimization and fix the code. Let's
   compiler care about low-level performance.

jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion,jmckaskill/subversion