Incremental improvements to path finding memory usage:

* Abort background path finding when closed or disconnected
* Exit pathfinding job thread if there are no requests left
* Don't bother creating the path find job if there are no requests
* Refactor to remove circular dependency between InfoSub and PathRequest

src/ripple/rpc/impl/TransactionSign.cpp

@@ -223,7 +223,8 @@ checkPayment(
             if (auto ledger = app.openLedger().current())
             {
                 Pathfinder pf(
-                    std::make_shared<RippleLineCache>(ledger),
+                    std::make_shared<RippleLineCache>(
+                        ledger, app.journal("RippleLineCache")),
                     srcAddressID,
                     *dstAccountID,
                     sendMax.issue().currency,