[Java] DictionaryEncoder doesn't crash when decoding index outside of Dictionary

从 DictionaryEncoder.decode 开始，并使用提供的 testReferencingIndexOutOfBounds 测试复现该行为。确认当编码后的索引等于字典值数量时会抛出带有预期消息的 IllegalArgumentException，同时有效索引仍能正常解码。

Describe the bug, including details regarding any error messages, version, and platform.

Background

When manually creating an encoded vector, with values referencing indices in a Dictionary, it is possible to have values equal to valueCount of the Dictionary vector i.e. one index out of bounds. This is interpreted as a null value in the Dictionary.

Example

Dictionary

Encoded Vector - 1

Encoded Vector - 2

Encoded Vector - 3

Test to reproduce the error

    @Test
    public void testReferencingIndexOutOfBounds() {
        // Index at which the original value will be stored at in the dictionary
        var encodedIndex = 0;
        // The encoded value that references an index in the dictionary
        var indexReferenced = 1;

        try (final IntVector encodedVector = new IntVector("encodings", allocator);
             final VarCharVector dictionaryVector = newVarCharVector("dict", allocator); ) {
            var originalValue = "Foo";
            dictionaryVector.allocateNew(1);
            dictionaryVector.setValueCount(1);
            dictionaryVector.set(encodedIndex, originalValue.getBytes(StandardCharsets.UTF_8));

            encodedVector.allocateNew(1);
            encodedVector.setValueCount(1);
            encodedVector.set(0, indexReferenced);

            Dictionary dictionary =
                    new Dictionary(dictionaryVector, new DictionaryEncoding(1L, false, null));

            try (ValueVector decoded = DictionaryEncoder.decode(encodedVector, dictionary)) {
                fail("There should be an exception when decoding index outside dictionary's range.");
            } catch (Exception e) {
                assertEquals("Provided dictionary does not contain value for index " + indexReferenced, e.getMessage());
            }
        }
    }