Replace two instances of N_DIGEST_ALGORITHMS.

These should have been N_COMMON_DIGEST_ALGORITHMS.

Fixes bug 18380; bug not in any released Tor.

src/or/dirvote.c

@@ -2121,7 +2121,7 @@ networkstatus_add_detached_signatures(networkstatus_t *target,
       *msg_out = "No digests for given consensus flavor";
       return -1;
     }
-    for (alg = DIGEST_SHA1; alg < N_DIGEST_ALGORITHMS; ++alg) {
+    for (alg = DIGEST_SHA1; alg < N_COMMON_DIGEST_ALGORITHMS; ++alg) {
       if (!tor_mem_is_zero(digests->d[alg], DIGEST256_LEN)) {
         if (fast_memeq(target->digests.d[alg], digests->d[alg],
                        DIGEST256_LEN)) {
@@ -2314,7 +2314,7 @@ networkstatus_get_detached_signatures(smartlist_t *consensuses)
 
     /* start with SHA256; we don't include SHA1 for anything but the basic
      * consensus. */
-    for (alg = DIGEST_SHA256; alg < N_DIGEST_ALGORITHMS; ++alg) {
+    for (alg = DIGEST_SHA256; alg < N_COMMON_DIGEST_ALGORITHMS; ++alg) {
       char d[HEX_DIGEST256_LEN+1];
       const char *alg_name =
         crypto_digest_algorithm_get_name(alg);