[fix](planner) fix ifnull and nvl function with one parameters exception message anbugious (#31808)

When ifnull or nvl funtion have only one parameter, nereids planner would throw an exception and go back to
original planner/ Original planner get secend parameter directly without check, so it return unexpected error message

fe/fe-core/src/main/java/org/apache/doris/analysis/FunctionCallExpr.java

@@ -1543,6 +1543,8 @@ public class FunctionCallExpr extends Expr {
 
         } else if (fnName.getFunction().equalsIgnoreCase("ifnull")
                 || fnName.getFunction().equalsIgnoreCase("nvl")) {
+            Preconditions.checkArgument(children != null && children.size() == 2,
+                    "The " + fnName + " function must have two params");
             Type[] childTypes = collectChildReturnTypes();
             Type assignmentCompatibleType = ScalarType.getAssignmentCompatibleType(childTypes[0], childTypes[1], true,
                     enableDecimal256);