Fix chunked prefill size validation for disabled state (#8973)

Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>

python/sglang/srt/server_args.py

@@ -1999,6 +1999,8 @@ class ServerArgs:
             ), "enable_mixed_chunk is required for speculative decoding"
 
         # Check chunked prefill
+        # Skip validation if chunked prefill is disabled (i.e., size <= 0).
+        if self.chunked_prefill_size > 0:
             assert (
                 self.chunked_prefill_size % self.page_size == 0
             ), "chunked_prefill_size must be divisible by page_size"