Fix an issue when clicking on a graph's first item
Fix an issue when clicking on a graph's first item

Clicking on the first chart is index=0, but the falsey check caused it   
to go to the default behaviour, which is to assume the user clicked on  
the last item in the graph.
misyak/plato-es6,mcanthony/plato,lorgiorepo/plato,es-analysis/plato,misyak/plato-es6,lorgiorepo/plato,Finanzchef24-GmbH/plato,vitormalencar/plato,jon-hall/es6-plato,es-analysis/plato,xebitstudios/plato,sljavi/plato,deedubs/es6-plato,tniswong/es6-plato,mcanthony/plato,jon-hall/es6-plato,smoakey/plato,smoakey/plato,smoakey/plato,FormidableLabs/fred-jones,jon-hall/es6-plato,xebitstudios/plato,sljavi/plato,jeffrey-l-turner/plato-1,sljavi/plato,mcanthony/plato,tniswong/es6-plato,xebitstudios/plato,Finanzchef24-GmbH/plato,lorgiorepo/plato,jeffrey-l-turner/plato-1,es-analysis/plato,ilanbiala/plato,jeffrey-l-turner/plato-1,deedubs/es6-plato,ilanbiala/plato,tniswong/es6-plato,Finanzchef24-GmbH/plato,ilanbiala/plato,misyak/plato-es6,vitormalencar/plato,vitormalencar/plato