Update llama_parse_json_element.py to fix error exception caused by certain PDF (#12402)

* Update llama_parse_json_element.py

Please refer to https://github.com/run-llama/llama_index/issues/12314

 for a detailed explanation of the bug fix.

* cr

---------

Co-authored-by: Haotian Zhang <socool.king@gmail.com>

llama-index-core/llama_index/core/node_parser/relational/llama_parse_json_element.py

@@ -260,7 +260,12 @@ class LlamaParseJsonNodeParser(BaseElementNodeParser):
                 and element.type == "text"
                 and merged_elements[-1].type == "text"
             ):
-                merged_elements[-1].element += "\n" + element.element
+                if isinstance(element.element, list):
+                    merged_elements[-1].element += "\n" + " ".join(
+                        str(e) for e in element.element
+                    )
+                else:
+                    merged_elements[-1].element += "\n" + element.element
             else:
                 merged_elements.append(element)
         elements = merged_elements