Fix unfunded offer not removed (RIPD-1298):

If the mantissas of two non-native amounts differ by less than 10, then
subtracting them leaves a result of zero. This can cause situations
where `a>b`, yet `a-b == 0`.

One consequence of this is unfunded offers were incorrectly left in
order books. The code would check if the offer would be
consumed (`amount in offer > amount needed`), assume it wouldn't be,
yet when `amount needed` was subtracted from `amount in offer` the
result was zero and the offer was unfunded. This unfunded offer
incorrectly remained on the order book.

This patch fixes this bug.

src/ripple/app/paths/impl/BookStep.cpp

@@ -412,7 +412,15 @@ BookStep<TIn, TOut>::revImp (
             result.in = sum(savedIns);
             result.out = out;
             this->consumeOffer (sb, offer, ofrAdjAmt, stpAdjAmt, ownerGivesAdj);
-            return false;
+
+            // When the mantissas of two iou amounts differ by less than ten, then
+            // subtracting them leaves a result of zero. This can cause the check for
+            // (stpAmt.out > remainingOut) to incorrectly think an offer will be funded
+            // after subtracting remainingIn.
+            if (amendmentRIPD1298(sb.parentCloseTime()))
+                return offer.fully_consumed();
+            else
+                return false;
         }
     };
 
@@ -561,6 +569,14 @@ BookStep<TIn, TOut>::fwdImp (
 
         remainingIn = in - result.in;
         this->consumeOffer (sb, offer, ofrAdjAmt, stpAdjAmt, ownerGivesAdj);
+
+        // When the mantissas of two iou amounts differ by less than ten, then
+        // subtracting them leaves a result of zero. This can cause the check for
+        // (stpAmt.in > remainingIn) to incorrectly think an offer will be funded
+        // after subtracting remainingIn.
+        if (amendmentRIPD1298(sb.parentCloseTime()))
+            processMore = processMore || offer.fully_consumed();
+
         return processMore;
     };