clones.js: 0 is different from undefined

Return undefined when the value is unknown. A 0 value may be meaningful.
The code has been changed by previous commits so that it can handle
undefined values.

browser/js/clone.js

@@ -160,7 +160,7 @@ Clone.prototype = {
         if (positions != null) {
             return positions['stop'] - positions['start'] + 1
         } else {
-            return 0;
+            return 'undefined';
         }
     },
 
@@ -506,7 +506,7 @@ Clone.prototype = {
         if (typeof this.seg != 'undefined' && typeof this.seg['3start'] != 'undefined'){
             return this.seg['3start']-this.seg['5end']-1
         }else{
-            return 0
+            return 'undefined'
         }
     },
     

browser/js/scatterPlot.js

@@ -739,7 +739,7 @@ ScatterPlot.prototype = {
                     try{
                         var v = fct(i);
                     }catch(e){}
-                    if (typeof v != "undefined" && v != 0){
+                    if (typeof v != "undefined" && v!= 'undefined'){
                         if (v<min || typeof min == "undefined") min = v;
                         if (v>max || typeof max == "undefined") max = v;
                     }