Update comments for threshold logic in GetAggregatePrice

Clarified comments regarding the threshold logic for erasing outdated prices.

src/libxrpl/tx/transactors/oracle/SetOracle.cpp

@@ -92,7 +92,7 @@ SetOracle::preclaim(PreclaimContext const& ctx)
         return !v || *v == (*sle)[field];
     };
 
-    std::uint32_t adjustReserve = 0;
+    std::int8_t adjustReserve = 0;
     if (sle)
     {
         // update

src/xrpld/rpc/handlers/GetAggregatePrice.cpp

@@ -218,6 +218,12 @@ doGetAggregatePrice(RPC::JsonContext& context)
         return result;
     }
 
+    // Get the ledger
+    std::shared_ptr<ReadView const> ledger;
+    result = RPC::lookupLedger(ledger, context);
+    if (!ledger)
+        return result;  // LCOV_EXCL_LINE
+
     // Collect the dataset into bimap keyed by lastUpdateTime and
     // STAmount (Number is int64 and price is uint64)
     Prices prices;
@@ -238,11 +244,6 @@ doGetAggregatePrice(RPC::JsonContext& context)
             return result;
         }
 
-        std::shared_ptr<ReadView const> ledger;
-        result = RPC::lookupLedger(ledger, context);
-        if (!ledger)
-            return result;  // LCOV_EXCL_LINE
-
         auto const sle = ledger->read(keylet::oracle(*account, *documentID));
         iteratePriceData(context, sle, [&](STObject const& node) {
             auto const& series = node.getFieldArray(sfPriceDataSeries);
@@ -284,8 +285,8 @@ doGetAggregatePrice(RPC::JsonContext& context)
     if (auto const threshold = std::get<std::uint32_t>(timeThreshold))
     {
         // threshold defines an acceptable range {max,min} of lastUpdateTime as
-        // {latestTime, latestTime - threshold}, the prices with lastUpdateTime
-        // greater than (latestTime - threshold) are erased.
+        // {latestTime, latestTime - threshold}. Prices with lastUpdateTime
+        // less than (latestTime - threshold) are erased (outdated prices).
         auto const oldestTime = prices.left.rbegin()->first;
         auto const upperBound = latestTime > threshold ? (latestTime - threshold) : oldestTime;
         if (upperBound > oldestTime)