pie: accept emptry string in helpers.getFirstFilled

Author: antoinerg

src/traces/pie/helpers.js

@@ -30,7 +30,7 @@ exports.getFirstFilled = function getFirstFilled(array, indices) {
     if(!Array.isArray(array)) return;
     for(var i = 0; i < indices.length; i++) {
         var v = array[indices[i]];
-        if(v || v === 0) return v;
+        if(v || v === 0 || v === '') return v;
     }
 };
 

src/traces/pie/plot.js

@@ -991,7 +991,7 @@ function formatSliceLabel(gd, pt, cd0) {
             pt.text = '';
         } else {
             var obj = makeTemplateVariables(pt);
-            var ptTx = Lib.castOption(trace, pt.i, 'text');
+            var ptTx = helpers.getFirstFilled(trace.text, pt.pts);
             if(isValidTextValue(ptTx) || ptTx === '') obj.text = ptTx;
             pt.text = Lib.texttemplateString(txt, obj, gd._fullLayout._d3locale, obj, trace._meta || {});
         }