coinstats: add coins_count

Also changes existing CCoinsStats attributes to be C++11 initialized.

src/node/coinstats.cpp

@@ -38,6 +38,7 @@ static void ApplyStats(CCoinsStats &stats, CHashWriter& ss, const uint256& hash,
 //! Calculate statistics about the unspent transaction output set
 bool GetUTXOStats(CCoinsView *view, CCoinsStats &stats)
 {
+    stats = CCoinsStats();
     std::unique_ptr<CCoinsViewCursor> pcursor(view->Cursor());
     assert(pcursor);
 
@@ -61,6 +62,7 @@ bool GetUTXOStats(CCoinsView *view, CCoinsStats &stats)
             }
             prevkey = key.hash;
             outputs[key.n] = std::move(coin);
+            stats.coins_count++;
         } else {
             return error("%s: unable to read value", __func__);
         }