Stifle an extraneous compile warning

Enclave/sort.cpp

@@ -82,7 +82,7 @@ void sort_mtobliv(threadid_t nthreads, uint8_t* items, uint16_t msg_size,
     // WaksmanNetwork with Nr <= Nw <= Na
     pthread_mutex_lock(&precomp_wns.mutex);
     std::optional<WaksmanNetwork> wn;
-    uint32_t Nw;
+    uint32_t Nw = 0;
     for (auto& N : precomp_wns.sized_wns) {
         if (N.first > Na) {
             printf("No precomputed WaksmanNetworks of size at most %u\n", Na);