resize the eventRect for single data points for tooltips to work

c3.js

@@ -2012,11 +2012,25 @@
                 rectW = function (d) {
                     var prevX = $$.getPrevX(d.index), nextX = $$.getNextX(d.index), dx = $$.data.xs[d.id][d.index],
                         w = ($$.x(nextX ? nextX : dx) - $$.x(prevX ? prevX : dx)) / 2;
+
+                    // if there this is a single data point make the eventRect full width (or height)
+                    if (prevX === null && nextX === null) {
+                        return config.axis_rotated ? $$.height : $$.width;
+                    }
+                    else {
                         return w < 0 ? 0 : w;
+                    }
                 };
                 rectX = function (d) {
-                    var prevX = $$.getPrevX(d.index), dx = $$.data.xs[d.id][d.index];
+                    var prevX = $$.getPrevX(d.index), nextX = $$.getNextX(d.index), dx = $$.data.xs[d.id][d.index];
+                    
+                    // if there this is a single data point position the eventRect at 0
+                    if (prevX === null && nextX === null) {
+                        return 0;
+                    }
+                    else {
                         return ($$.x(dx) + $$.x(prevX ? prevX : dx)) / 2;
+                    }
                 };
             } else {
                 rectW = $$.getEventRectWidth();

src/interaction.js

@@ -62,11 +62,25 @@ c3_chart_internal_fn.updateEventRect = function (eventRectUpdate) {
             rectW = function (d) {
                 var prevX = $$.getPrevX(d.index), nextX = $$.getNextX(d.index), dx = $$.data.xs[d.id][d.index],
                     w = ($$.x(nextX ? nextX : dx) - $$.x(prevX ? prevX : dx)) / 2;
+
+                // if there this is a single data point make the eventRect full width (or height)
+                if (prevX === null && nextX === null) {
+                    return config.axis_rotated ? $$.height : $$.width;
+                }
+                else {
                     return w < 0 ? 0 : w;
+                }
             };
             rectX = function (d) {
-                var prevX = $$.getPrevX(d.index), dx = $$.data.xs[d.id][d.index];
+                var prevX = $$.getPrevX(d.index), nextX = $$.getNextX(d.index), dx = $$.data.xs[d.id][d.index];
+                
+                // if there this is a single data point position the eventRect at 0
+                if (prevX === null && nextX === null) {
+                    return 0;
+                }
+                else {
                     return ($$.x(dx) + $$.x(prevX ? prevX : dx)) / 2;
+                }
             };
         } else {
             rectW = $$.getEventRectWidth();