Standardize code to use name,null when no parent, remove null,name path

Author: kripken

src/library_wasmfs.js

@@ -50,7 +50,7 @@ var WasmfsLibrary = {
     createDataFile: function(parent, name, data, canRead, canWrite, canOwn) {
       // Data files must be cached until the file system itself has been initialized.
       var mode = FS.getMode(canRead, canWrite);
-      var pathName = parent ? parent + '/' + name : name;
+      var pathName = name ? parent + '/' + name : parent;
       wasmFS$preloadedFiles.push({pathName: pathName, fileData: data, mode: mode});
     },
     createPath: function(parent, path, canRead, canWrite) {

tools/file_packager.py

@@ -649,7 +649,7 @@ def generate_js(data_target, data_files, metadata):
         var content = HEAPU32[start32++];
         var name = UTF8ToString(name_addr)
         // canOwn this data in the filesystem, it is a slice of wasm memory that will never change
-        Module['FS_createDataFile'](undefined, name, HEAP8.subarray(content, content + len), true, true, true);
+        Module['FS_createDataFile'](name, null, HEAP8.subarray(content, content + len), true, true, true);
       } while (HEAPU32[start32]);'''
     else:
       err('--obj-output is recommended when using --embed.  This outputs an object file for linking directly into your application is more effecient than JS encoding')