Fix a few JS warnings that pop into the console

data/aggregate.js

@@ -286,6 +286,7 @@ function GraphEdge(source, target, connection) {
   if (connection) {
     this.cookieCount = connection.cookie ? 1 : 0;
   }
+  return this;
   // console.log('edge: %s', this.name);
 }
 GraphEdge.prototype.lastAccess = function () {

data/svgdataset.js

@@ -26,9 +26,11 @@ function svgdataset(elem) {
         return value;
       }
     } else {
-      elem.setAttribute(dataKeyToAttr(key), JSON.stringify(value));
+      var s = JSON.stringify(value);
+      elem.setAttribute(dataKeyToAttr(key), s);
+      return s;
     }
-  }
+  };
   // Create read-only shortcuts for convenience
   Array.prototype.forEach.call(elem.attributes, function (attr) {
     if (attr.name.startsWith('data-')) {

data/ui.js

@@ -182,6 +182,7 @@ global.getZoom = function getZoom(canvas) {
   } catch (e) {
     console.log('error in getZoom, called with %o instead of an element');
     console.log('Caller: %o', caller);
+    return null;
   }
 }