fix minor compiler warning

lib/multi.c

@@ -1083,7 +1083,7 @@ static void singlesocket(struct Curl_multi *multi,
             continue;
         }
 
-        action = ((current.action & GETSOCK_READSOCK(i))?CURL_POLL_IN:0) |
+        action = ((current.action & GETSOCK_READSOCK(i))?CURL_POLL_IN:0) +
           ((current.action & GETSOCK_WRITESOCK(i))?CURL_POLL_OUT:0);
       }