Fix npe for copyNecessaryFilesFromCurrentPackage

Author: DordeDimitrijev

android/app/src/main/java/com/microsoft/codepush/react/CodePushUpdateUtils.java

@@ -98,7 +98,11 @@ private static String computeHash(InputStream dataStream) {
  }
 
  public static void copyNecessaryFilesFromCurrentPackage(String diffManifestFilePath, String currentPackageFolderPath, String newPackageFolderPath) throws IOException {
- FileUtils.copyDirectoryContents(currentPackageFolderPath, newPackageFolderPath); 
+ if (currentPackageFolderPath == null || !new File(currentPackageFolderPath).exists()) {
+ CodePushUtils.log("Unable to copy files from current package during diff update, because currentPackageFolderPath is invalid.");
+ return;
+ }
+ FileUtils.copyDirectoryContents(currentPackageFolderPath, newPackageFolderPath); 
  JSONObject diffManifest = CodePushUtils.getJsonObjectFromFile(diffManifestFilePath);
  try {
  JSONArray deletedFiles = diffManifest.getJSONArray("deletedFiles");