fix a fuzzer detected corner case

src/core/lib/channel/http_server_filter.c

@@ -209,6 +209,7 @@ static grpc_error *server_filter_incoming_metadata(grpc_exec_ctx *exec_ctx,
     for (offset = 0; *path_ptr != k_query_separator[0] && offset < path_length;
          path_ptr++, offset++)
       ;
+    if (offset < path_length) {
       grpc_slice query_slice =
           grpc_slice_sub(path_slice, offset + 1, path_length);
 
@@ -229,6 +230,9 @@ static grpc_error *server_filter_incoming_metadata(grpc_exec_ctx *exec_ctx,
       grpc_slice_buffer_stream_init(&calld->read_stream,
                                     &calld->read_slice_buffer, 0);
       calld->seen_path_with_query = true;
+    } else {
+      gpr_log(GPR_ERROR, "GET request without QUERY");
+    }
   }
 
   if (b->idx.named.host != NULL && b->idx.named.authority == NULL) {