community[patch]: document_loaders: modified athena key logic to handle s3 uris without a prefix (#17526)

https://github.com/langchain-ai/langchain/issues/17525

### Example Code

```python
from langchain_community.document_loaders.athena import AthenaLoader

database_name = "database"
s3_output_path = "s3://bucket-no-prefix"
query="""SELECT 
  CAST(extract(hour FROM current_timestamp) AS INTEGER) AS current_hour,
  CAST(extract(minute FROM current_timestamp) AS INTEGER) AS current_minute,
  CAST(extract(second FROM current_timestamp) AS INTEGER) AS current_second;
"""
profile_name = "AdministratorAccess"

loader = AthenaLoader(
    query=query,
    database=database_name,
    s3_output_uri=s3_output_path,
    profile_name=profile_name,
)

documents = loader.load()
print(documents)
```



### Error Message and Stack Trace (if applicable)

NoSuchKey: An error occurred (NoSuchKey) when calling the GetObject
operation: The specified key does not exist

### Description

Athena Loader errors when result s3 bucket uri has no prefix. The Loader
instance call results in a "NoSuchKey: An error occurred (NoSuchKey)
when calling the GetObject operation: The specified key does not exist."
error.

If s3_output_path contains a prefix like:

```python
s3_output_path = "s3://bucket-with-prefix/prefix"
```

Execution works without an error.

## Suggested solution

Modify:

```python
key = "/".join(tokens[1:]) + "/" + query_execution_id + ".csv"
```

to

```python
key = "/".join(tokens[1:]) + ("/" if tokens[1:] else "") + query_execution_id + ".csv"
```


9e8a3fc4ff/libs/community/langchain_community/document_loaders/athena.py (L128)


### System Info


System Information
------------------
> OS:  Darwin
> OS Version: Darwin Kernel Version 22.6.0: Fri Sep 15 13:41:30 PDT
2023; root:xnu-8796.141.3.700.8~1/RELEASE_ARM64_T8103
> Python Version:  3.9.9 (main, Jan  9 2023, 11:42:03) 
[Clang 14.0.0 (clang-1400.0.29.102)]

Package Information
-------------------
> langchain_core: 0.1.23
> langchain: 0.1.7
> langchain_community: 0.0.20
> langsmith: 0.0.87
> langchain_openai: 0.0.6
> langchainhub: 0.1.14

Packages not installed (Not Necessarily a Problem)
--------------------------------------------------
The following packages were not found:

> langgraph
> langserve

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/community/langchain_community/document_loaders/athena.py

@@ -125,7 +125,7 @@ class AthenaLoader(BaseLoader):
             self._remove_suffix(output_uri, "/"), "s3://"
         ).split("/")
         bucket = tokens[0]
-        key = "/".join(tokens[1:]) + "/" + query_execution_id + ".csv"
+        key = "/".join(tokens[1:] + [query_execution_id]) + ".csv"
 
         obj = self.s3_client.get_object(Bucket=bucket, Key=key)
         df = pd.read_csv(io.BytesIO(obj["Body"].read()), encoding="utf8")