Do not crash if the sources of a move or copy API call is empty.
Do not crash if the sources of a move or copy API call is empty.

* subversion/libsvn_client/copy.c (try_copy):
   Add assertion that the source array contains at least one element.


git-svn-id: f8a4e5e023278da1e04e203c7fe051e3c4285d88@1526103 13f79535-47bb-0310-9956-ffa450edef68

YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion,YueLinHo/Subversion