Correctly handle partial success in consensus diff calculation.

Previously, if store_multiple() reported a partial success, we would
store all the handles it gave us as if they had succeeded.  But it's
possible for the diff to be only partially successful -- for
example, if LZMA failed but the other compressors succeeded.

Fixes bug 24086; bugfix on 0.3.1.1-alpha.

changes/bug24086

@@ -0,0 +1,7 @@
+  o Minor bugfixes (directory cache):
+    - When a consensus diff calculation is only partially successful, only
+      record the successful parts as having succeeded. Partial success
+      can happen if (for example) one compression method fails but
+      the others succeed. Previously we misrecorded all the calculations as
+      having succeeded, which would later cause a nonfatal assertion failure.
+      Fixes bug 24086; bugfix on 0.3.1.1-alpha.

src/or/consdiffmgr.c

@@ -1589,8 +1589,13 @@ consensus_diff_worker_replyfn(void *work_)
   for (u = 0; u < ARRAY_LENGTH(handles); ++u) {
     compress_method_t method = compress_diffs_with[u];
     if (cache) {
-      cdm_diff_ht_set_status(flav, from_sha3, to_sha3, method, status,
-                             handles[u]);
+      consensus_cache_entry_handle_t *h = handles[u];
+      int this_status = status;
+      if (h == NULL) {
+        this_status = CDM_DIFF_ERROR;
+      }
+      tor_assert_nonfatal(h != NULL || this_status == CDM_DIFF_ERROR);
+      cdm_diff_ht_set_status(flav, from_sha3, to_sha3, method, this_status, h);
     } else {
       consensus_cache_entry_handle_free(handles[u]);
     }