[FEAT] JSON constrained support (#1125)

Co-authored-by: Yineng Zhang <me@zhyncs.com>

python/sglang/srt/managers/schedule_batch.py

@@ -268,7 +268,14 @@ class Req:
 
         all_text = self.origin_input_text + self.decoded_text + jump_forward_str
         all_ids = self.tokenizer.encode(all_text)
+        if not all_ids:
+            warnings.warn("Encoded all_text resulted in empty all_ids")
+            return False
+
         prompt_tokens = len(self.origin_input_ids_unpadded)
+        if prompt_tokens > len(all_ids):
+            warnings.warn("prompt_tokens is larger than encoded all_ids")
+            return False
 
         if all_ids[prompt_tokens - 1] != self.origin_input_ids_unpadded[-1]:
             # TODO(lsyin): fix token fusion