fix: bugs while testing the example

examples/data/multi_modal/1.jpg

examples/data/multi_modal/2.jpg

examples/data/multi_modal/3.jpg

examples/data/multi_modal/60.jpg

examples/data/multi_modal/61.jpg

examples/data/multi_modal/62.jpg

examples/data/multi_modal/San Francisco.txt

examples/data/multi_modal/Vincent van Gogh.txt

examples/multiModal.ts

packages/core/src/Node.ts

packages/core/src/NodeParser.ts

packages/core/src/embeddings/MultiModalEmbedding.ts

...ages/core/src/indices/vectorStore/VectorIndexRetriever.ts

packages/core/src/indices/vectorStore/VectorStoreIndex.ts

packages/core/src/readers/ImageReader.ts