Fix data label position when all the data set is Zero

When all the data set is zero the label should be in the above of the y
axis

c3.js

@@ -2036,6 +2036,8 @@
         var $$ = this, config = $$.config,
             ids = $$.d3.keys(data[0]).filter($$.isNotX, $$),
             xs = $$.d3.keys(data[0]).filter($$.isX, $$),
+            zeroUnderYAxis = true,
+            allZero = true,
             targets;
 
         $$.allDataIsNegative = true;
@@ -2095,8 +2097,12 @@
                         x = undefined;
                     }
 
+                    if(value !== null && value !== 0) {
+                        allZero = false;
+                    }
+
                     if(value > 0) {
-                        $$.allDataIsNegative = false;
+                        zeroUnderYAxis = false;
                     }
 
                     return {x: x, value: value, id: convertedId};
@@ -2126,6 +2132,12 @@
             });
         });
 
+        if(allZero) {
+            zeroUnderYAxis = false;
+        }
+
+        $$.zeroUnderYAxis = zeroUnderYAxis;
+
         // set target types
         if (config.data_type) {
             $$.setTargetType($$.mapToIds(targets).filter(function (id) { return ! (id in config.data_types); }), config.data_type);
@@ -3361,7 +3373,7 @@
             yPos = (points[0][0] + points[2][0] + box.height * 0.6) / 2;
         } else {
             yPos = points[2][1];
-            if (d.value < 0  || (d.value === 0 && $$.allDataIsNegative)) {
+            if (d.value < 0  || (d.value === 0 && $$.zeroUnderYAxis)) {
                 yPos += box.height;
                 if ($$.isBarType(d) && $$.isSafari()) {
                     yPos -= 3;

src/data.convert.js

@@ -96,6 +96,8 @@ c3_chart_internal_fn.convertDataToTargets = function (data, appendXs) {
     var $$ = this, config = $$.config,
         ids = $$.d3.keys(data[0]).filter($$.isNotX, $$),
         xs = $$.d3.keys(data[0]).filter($$.isX, $$),
+        zeroUnderYAxis = true,
+        allZero = true,
         targets;
 
     $$.allDataIsNegative = true;
@@ -155,8 +157,12 @@ c3_chart_internal_fn.convertDataToTargets = function (data, appendXs) {
                     x = undefined;
                 }
 
+                if(value !== null && value !== 0) {
+                    allZero = false;
+                }
+
                 if(value > 0) {
-                    $$.allDataIsNegative = false;
+                    zeroUnderYAxis = false;
                 }
 
                 return {x: x, value: value, id: convertedId};
@@ -186,6 +192,12 @@ c3_chart_internal_fn.convertDataToTargets = function (data, appendXs) {
         });
     });
 
+    if(allZero) {
+        zeroUnderYAxis = false;
+    }
+
+    $$.zeroUnderYAxis = zeroUnderYAxis;
+
     // set target types
     if (config.data_type) {
         $$.setTargetType($$.mapToIds(targets).filter(function (id) { return ! (id in config.data_types); }), config.data_type);

src/text.js

@@ -98,7 +98,7 @@ c3_chart_internal_fn.getYForText = function (points, d, textElement) {
         yPos = (points[0][0] + points[2][0] + box.height * 0.6) / 2;
     } else {
         yPos = points[2][1];
-        if (d.value < 0  || (d.value === 0 && $$.allDataIsNegative)) {
+        if (d.value < 0  || (d.value === 0 && $$.zeroUnderYAxis)) {
             yPos += box.height;
             if ($$.isBarType(d) && $$.isSafari()) {
                 yPos -= 3;