Fix for IBE-198, scratch-analysis should be able to deal with a JSON project file that does not contain extensions data

lib/sb3.js

@@ -120,8 +120,8 @@ const blocks = function (targets) {
 
 const extensions = function (list) {
     return {
-        count: list.length,
-        id: list
+        count: (typeof list === 'object' ? list.length : 0),
+        id: (typeof list === 'object' ? list : [])
     };
 };