community: vectorstores.kdbai - Added support for when no docs are present (#18103)

- **Description:** By default it expects a list but that's not the case
in corner scenarios when there is no document ingested(use case:
Bootstrap application).
\
Hence added as check, if the instance is panda Dataframe instead of list
then it will procced with return immediately.

- **Issue:** NA
- **Dependencies:** NA
- **Twitter handle:**  jaskiratsingh1

---------

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

libs/community/langchain_community/vectorstores/kdbai.py

@@ -217,10 +217,12 @@ class KDBAI(VectorStore):
         """
         if "n" in kwargs:
             k = kwargs.pop("n")
-        matches = self._table.search(vectors=[embedding], n=k, filter=filter, **kwargs)[
-            0
-        ]
-        docs = []
+        matches = self._table.search(vectors=[embedding], n=k, filter=filter, **kwargs)
+        docs: list = []
+        if isinstance(matches, list):
+            matches = matches[0]
+        else:
+            return docs
         for row in matches.to_dict(orient="records"):
             text = row.pop("text")
             score = row.pop("__nn_distance")