XML RPC API method getIssuesFromTextSearchWithProject does not allow empty search terms

The method getIssuesFromTextSearchWithProject of the XML RPC service and the soap service used to allow empty search terms. If the method is called with an empty search term it constructs a JQL query which contains the condition: text ~ "". The empty string is not supported for the text clause.

This is causing problems with clients expecting to be able to provide no/empty search terms.

The SearchService of the rpc plugin should not add the condition if no search terms are provided.