Unicode characters outside of string literals trigger 500 error

minor bug, but issuing a query like;

`select 1 as 😀`

will trigger a 500 response from the plugin;
`{"message":"An error occurred within the plugin","messageId":"plugin.downstreamError","statusCode":500,"traceID":""}`

whereas it should simpy return the ClickHouse exception;

`Unrecognized token: Syntax error: failed at position 13 (😀):`
