perf: allow zero chunk overlap in recursive chunker (#4258)

* Allow zero chunk overlap

* Validate recursive chunking bounds

astrbot/core/knowledge_base/chunking/recursive.py

@@ -149,8 +149,16 @@ class RecursiveCharacterChunker(BaseChunker):
             分割后的文本块列表
 
         """
-        chunk_size = chunk_size or self.chunk_size
-        overlap = overlap or self.chunk_overlap
+        if chunk_size is None:
+            chunk_size = self.chunk_size
+        if overlap is None:
+            overlap = self.chunk_overlap
+        if chunk_size <= 0:
+            raise ValueError("chunk_size must be greater than 0")
+        if overlap < 0:
+            raise ValueError("chunk_overlap must be non-negative")
+        if overlap >= chunk_size:
+            raise ValueError("chunk_overlap must be less than chunk_size")
         result = []
         for i in range(0, len(text), chunk_size - overlap):
             end = min(i + chunk_size, len(text))