refactor: improve checking of path lengths (XRPLF#4519)

Improve the checking of the path lengths during Payments. Previously,
the code that did the check of the payment path lengths was sometimes
executed, but without any effect. This changes it to only check when it
matters, and to not make unnecessary copies of the path vectors.

src/ripple/app/tx/impl/Payment.cpp

@@ -270,27 +270,17 @@ Payment::preclaim(PreclaimContext const& ctx)
         return tecDST_TAG_NEEDED;
     }
 
-    if (paths || sendMax || !saDstAmount.native())
+    // Payment with at least one intermediate step and uses transitive balances.
+    if ((paths || sendMax || !saDstAmount.native()) && ctx.view.open())
     {
-        // Ripple payment with at least one intermediate step and uses
-        // transitive balances.
-
-        // Copy paths into an editable class.
-        STPathSet const spsPaths = ctx.tx.getFieldPathSet(sfPaths);
+        STPathSet const& paths = ctx.tx.getFieldPathSet(sfPaths);
 
-        auto pathTooBig = spsPaths.size() > MaxPathSize;
-
-        if (!pathTooBig)
-            for (auto const& path : spsPaths)
-                if (path.size() > MaxPathLength)
-                {
-                    pathTooBig = true;
-                    break;
-                }
-
-        if (ctx.view.open() && pathTooBig)
+        if (paths.size() > MaxPathSize ||
+            std::any_of(paths.begin(), paths.end(), [](STPath const& path) {
+                return path.size() > MaxPathLength;
+            }))
         {
-            return telBAD_PATH_COUNT;  // Too many paths for proposed ledger.
+            return telBAD_PATH_COUNT;
         }
     }
 
@@ -384,9 +374,6 @@ Payment::doApply()
             }
         }
 
-        // Copy paths into an editable class.
-        STPathSet spsPaths = ctx_.tx.getFieldPathSet(sfPaths);
-
         path::RippleCalc::Input rcInput;
         rcInput.partialPaymentAllowed = partialPaymentAllowed;
         rcInput.defaultPathsAllowed = defaultPathsAllowed;
@@ -404,7 +391,7 @@ Payment::doApply()
                 saDstAmount,
                 uDstAccountID,
                 account_,
-                spsPaths,
+                ctx_.tx.getFieldPathSet(sfPaths),
                 ctx_.app.logs(),
                 &rcInput);
             // VFALCO NOTE We might not need to apply, depending