CB-14181: (android) Fix bug - Cannot read property 'filesystemName' of null (#235)

CB-14181: (android)  fix: Cannot read property 'filesystemName' of null

fix error :

Error in Success callbackId: File1539060614 : TypeError: Cannot read property 'filesystemName' of null
cordova.js:314 Uncaught TypeError: Cannot read property 'filesystemName' of null

The `fsRoot` might be null. reproduced with latest cordova on android emulator.

* fix: eslint
diff --git a/www/fileSystems-roots.js b/www/fileSystems-roots.js
index 9a3fc7a..b15adbd 100644
--- a/www/fileSystems-roots.js
+++ b/www/fileSystems-roots.js
@@ -30,8 +30,10 @@
         fsMap = {};
         for (var i = 0; i < response.length; ++i) {
             var fsRoot = response[i];
-            var fs = new FileSystem(fsRoot.filesystemName, fsRoot);
-            fsMap[fs.name] = fs;
+            if (fsRoot) {
+                var fs = new FileSystem(fsRoot.filesystemName, fsRoot);
+                fsMap[fs.name] = fs;
+            }
         }
         callback(fsMap[name]);
     }