[vislibRenderbot] don't give the vislib empty chartData

Fix for #2148 

The vislib requires that chartData include either a list of charts, or a single table. When no data was found, no tables were created and the vislib would [throw a TypeError](https://github.com/elasticsearch/kibana/blob/7bfb68cd24ed42b1b257682f93c50cd8d73e2520/src/kibana/components/vislib/components/zero_injection/inject_zeros.js#L32). This change has `buildChartData` instead mimic an empty table if there are no results.