refactor: restructure getRequestRouting per dkropachev's corrected suggestion

Move null guard for defaultLwtRequestRoutingMethod to the call site in
newQueryPlan, keeping getRequestRouting() focused on routing logic only:
- isLWT() -> return defaultLwtRequestRoutingMethod immediately
- serial effective CL -> return defaultLwtRequestRoutingMethod
- otherwise -> REGULAR

Author: nikagra

driver-core/src/main/java/com/datastax/driver/core/policies/TokenAwarePolicy.java

@@ -438,7 +438,11 @@ public Iterator<Host> newQueryPlan(final String loggedKeyspace, final Statement
         clusterMetadata.getReplicasList(
             Metadata.quote(keyspace), tableName, statement.getPartitioner(), partitionKey);
 
-    switch (getRequestRouting(statement)) {
+    QueryOptions.RequestRoutingMethod routing =
+        defaultLwtRequestRoutingMethod != null
+            ? getRequestRouting(statement)
+            : QueryOptions.RequestRoutingMethod.REGULAR;
+    switch (routing) {
       case PRESERVE_REPLICA_ORDER:
         return newQueryPlanPreserveReplicaOrder(keyspace, statement, replicas);
       case REGULAR:
@@ -470,14 +474,14 @@ private ColumnDefinitions getRoutingVariables(Statement statement) {
   }
 
   private QueryOptions.RequestRoutingMethod getRequestRouting(Statement statement) {
-    if (defaultLwtRequestRoutingMethod == null) {
-      return QueryOptions.RequestRoutingMethod.REGULAR;
-    }
-    ConsistencyLevel cl = statement.getConsistencyLevel();
-    if (cl == null) {
-      cl = queryOptions.getConsistencyLevel();
+    if (statement.isLWT()) {
+      return defaultLwtRequestRoutingMethod;
     }
-    if (statement.isLWT() || (cl != null && cl.isSerial())) {
+    ConsistencyLevel cl =
+        statement.getConsistencyLevel() != null
+            ? statement.getConsistencyLevel()
+            : queryOptions.getConsistencyLevel();
+    if (cl != null && cl.isSerial()) {
       return defaultLwtRequestRoutingMethod;
     }
     return QueryOptions.RequestRoutingMethod.REGULAR;