merged create_torrent fix from RC_0_16

ChangeLog

@@ -25,6 +25,7 @@
 	* fix uTP edge case where udp socket buffer fills up
 	* fix nagle implementation in uTP
 
+	* add some error handling to set_piece_hashes()
 	* fix completed-on timestamp to not be clobbered on each startup
 	* fix deadlock caused by some UDP tracker failures
 	* fix potential integer overflow issue in timers on windows

src/create_torrent.cpp

@@ -200,6 +200,12 @@ namespace libtorrent
 		std::string const& path = p;
 #endif
 
+		if (t.files().num_files() == 0)
+		{
+			ec = error_code(errors::no_files_in_torrent, get_libtorrent_category());
+			return;
+		}
+
 		boost::scoped_ptr<storage_interface> st(
 			default_storage_constructor(const_cast<file_storage&>(t.files()), 0, path, fp
 			, std::vector<boost::uint8_t>()));