fix: Fixes pdf cut type None bug by introducting default cut type (#1044)

…cut type

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## Description
 Fixes pdf cut type None bug by introducting default cut type

## DCO Affirmation
I affirm that all code in every commit of this pull request conforms to
the terms of the Topoteretes Developer Certificate of Origin.

cognee/tasks/chunks/chunk_by_paragraph.py

@@ -31,7 +31,7 @@ def chunk_by_paragraph(
     current_chunk = ""
     chunk_index = 0
     paragraph_ids = []
-    last_cut_type = None
+    last_cut_type = "default"
     current_chunk_size = 0
 
     for paragraph_id, sentence, sentence_size, end_type in chunk_by_sentence(
@@ -77,6 +77,9 @@ def chunk_by_paragraph(
             current_chunk_size = 0
             chunk_index += 1
 
+        if not end_type:
+            end_type = "default"
+
         last_cut_type = end_type
 
     # Yield any remaining text