rpc: convert distribution to cumulative after caching

This avoids double conversion on a later cache hit

src/rpc/core_rpc_server.cpp

@@ -2117,12 +2117,6 @@ namespace cryptonote
           if (offset <= req.to_height && req.to_height - offset + 1 < distribution.size())
             distribution.resize(req.to_height - offset + 1);
         }
-        if (req.cumulative)
-        {
-          distribution[0] += base;
-          for (size_t n = 1; n < distribution.size(); ++n)
-            distribution[n] += distribution[n-1];
-        }
 
         if (amount == 0)
         {
@@ -2134,6 +2128,13 @@ namespace cryptonote
           d.cached = true;
         }
 
+        if (req.cumulative)
+        {
+          distribution[0] += base;
+          for (size_t n = 1; n < distribution.size(); ++n)
+            distribution[n] += distribution[n-1];
+        }
+
         res.distributions.push_back({amount, start_height, std::move(distribution), base});
       }
     }