[Fix](Nereids) fix fe ut failed cause of getting statement context (#29683)

Problem:
fe ut failed cause of null pointer error
Cause:
fe ut getting statement context from connection context failed
Resolved:
add null pointer judgement

fe/fe-core/src/main/java/org/apache/doris/nereids/parser/LogicalPlanBuilder.java

@@ -2773,6 +2773,7 @@ public class LogicalPlanBuilder extends DorisParserBaseVisitor<Object> {
 
             }
             if (distributeHint.distributeType != DistributeType.NONE
+                    && ConnectContext.get().getStatementContext() != null
                     && !ConnectContext.get().getStatementContext().getHints().contains(distributeHint)) {
                 ConnectContext.get().getStatementContext().addHint(distributeHint);
             }