Fix data: protocol

Increment conn->from by the length of the data so that when
abort_connection calls normalize_cache_entry, it doesn't truncate the
cache entry to 0 length.

src/protocol/data.c

@@ -157,6 +157,7 @@ data_protocol_handler(struct connection *conn)
 		int datalen = strlen(data);
 
 		add_fragment(cached, conn->from, data, datalen);
+		conn->from += datalen;
 	}
 
 	mem_free(data);