[fix](Nereids) fix split part with delim not exist in source string (#48895)

### What problem does this PR solve?

Related PR: #40441

Problem Summary:

if source string do not contains delim, split_part should return NULL

Author: LiBinfeng

fe/fe-core/src/main/java/org/apache/doris/nereids/trees/expressions/functions/executable/StringArithmetic.java

@@ -699,6 +699,9 @@ public static Expression splitPart(StringLikeLiteral first, StringLikeLiteral ch
                 return new NullLiteral(first.getDataType());
             }
         }
+        if (!first.getValue().contains(chr.getValue())) {
+            return new NullLiteral(first.getDataType());
+        }
         String separator = chr.getValue();
         String[] parts;
         if (number.getValue() < 0) {

regression-test/suites/nereids_p0/expression/fold_constant/fold_constant_string_arithmatic.groovy

@@ -592,6 +592,9 @@ suite("fold_constant_string_arithmatic") {
     testFoldConst("SELECT split_part('a..b\$\$c||d((e))f[[g{{h^^i??j**k++l\\\\m','**', 2)")
     testFoldConst("SELECT split_part('a..b\$\$c||d((e))f[[g{{h^^i??j**k++l\\\\m','++', 2)")
     testFoldConst("SELECT split_part('a..b\$\$c||d((e))f[[g{{h^^i??j**k++l\\\\m','\\\\', 2)")
+    testFoldConst("select split_part('abc', ':', -1)")
+    testFoldConst("select split_part('abc', ':', 0)")
+    testFoldConst("select split_part('abc', ':', 1)")
 
     // starts_with
     testFoldConst("select starts_with('hello world','hello')")