Fix crash when svn_client_lock or _unlock is passed an empty array.
Fix crash when svn_client_lock or _unlock is passed an empty array.

Suggested by: Stefan Kúng <steveking@gmx.ch>

* subversion/libsvn_client/locking_commands.c
  (svn_client_lock, svn_client_unlock): Just return if there are no targets.

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