Fix segfault in ra_get_log_locations compatibility code, triggered by running merge_tests #74 or merge_authz_tests #1 against a 1.4.x DAV server.  (Probably also would trigger if this command was ever issued against a rev with no changed paths or with no *readable* changed paths.)
Fix segfault in ra_get_log_locations compatibility code, triggered by
running merge_tests #74 or merge_authz_tests #1 against a 1.4.x DAV
server.  (Probably also would trigger if this command was ever issued
against a rev with no changed paths or with no *readable* changed
paths.)

* subversion/libsvn_ra/compat.c
  (prev_log_path): Deal with the case that changed_paths is NULL (by
   treating it as equivalent to empty).

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