fix mem error in to_base64_json

alloc space for newline in encode buffer

src/libs/conduit/Node.cpp

@@ -10608,7 +10608,7 @@ Node::to_base64_json(std::ostream &os,
     // use libb64 to encode the data
     index_t nbytes = n.schema().total_bytes();
     Node bb64_data;
-    bb64_data.set(DataType::char8_str(nbytes*2));
+    bb64_data.set(DataType::char8_str(nbytes*2+1));
 
     const char *src_ptr = (const char*)n.data_ptr();
     char *dest_ptr       = (char*)bb64_data.data_ptr();