Fixed bug spotted by Usman
Fixed bug spotted by Usman

https://code.google.com/p/moose-technology/issues/detail?id=1122

The following script does not trigger an error:
grapher := RTGrapher new
		extent: 300 @ 200;
		title: 'testing zero values';
		yourself.
	ds := RTDataSet new.
	ds	dotShape ellipse color: (Color red alpha: 0.5); size: 10.
	ds points: {0->0. 0->0};
		connectColor: (Color red alpha: 0.5);
		y: #value;
		x: #key;
		highlightIf: [:each | true] using: #value.
	grapher add: ds.
	grapher axisY decimal: 0; title: 'asdasd'.
	grapher axisX
		labelRotation: -30;
		title: '';
		numberOfLabels: 2.
		grapher build.


Former-commit-id: f06973a91af894bf7aeb8e8393d88398edaf2687
ObjectProfile/Roassal2